Auto merge of #14848 - bzbarsky:initial-styles, r=bholley

Stop using global initial styles for stylo; the initial styles need to be per-document

<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix https://bugzilla.mozilla.org/show_bug.cgi?id=1298588

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests on the servo side because behavior is unchanged.  Gecko-side tests probably exist.

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
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20 files changed, 287 insertions, 152 deletions

diff --git a/components/layout/construct.rs b/components/layout/construct.rs
index 660d4f64834..7c039d38729 100644
--- a/components/layout/construct.rs
+++ b/components/layout/construct.rs
@@ -54,7 +54,6 @@ use style::logical_geometry::Direction;
 use style::properties::{self, ServoComputedValues};
 use style::selector_parser::{PseudoElement, RestyleDamage};
 use style::servo::restyle_damage::{BUBBLE_ISIZES, RECONSTRUCT_FLOW};
-use style::stylist::Stylist;
 use style::values::Either;
 use table::TableFlow;
 use table_caption::TableCaptionFlow;
@@ -470,7 +469,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
         }
 
         inline_flow_ref.finish();
-        legalizer.add_child(&self.style_context().stylist, flow, inline_flow_ref)
+        legalizer.add_child(self.style_context(), flow, inline_flow_ref)
     }
 
     fn build_block_flow_using_construction_result_of_child(
@@ -503,7 +502,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                                                             legalizer,
                                                             node);
                     }
-                    legalizer.add_child(&self.style_context().stylist, flow, kid_flow)
+                    legalizer.add_child(self.style_context(), flow, kid_flow)
                 }
                 abs_descendants.push_descendants(kid_abs_descendants);
             }
@@ -537,7 +536,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                                                         node);
 
                     // Push the flow generated by the {ib} split onto our list of flows.
-                    legalizer.add_child(&self.style_context().stylist, flow, kid_flow)
+                    legalizer.add_child(self.style_context(), flow, kid_flow)
                 }
 
                 // Add the fragments to the list we're maintaining.
@@ -662,7 +661,8 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
             if node_is_input_or_text_area {
                 style = self.style_context()
                             .stylist
-                            .style_for_anonymous_box(&PseudoElement::ServoInputText, &style)
+                            .style_for_anonymous_box(&PseudoElement::ServoInputText, &style,
+                                                     &self.style_context().default_computed_values)
             }
 
             self.create_fragments_for_node_text_content(&mut initial_fragments, node, &style)
@@ -1094,7 +1094,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
         let wrapper_style = self.style_context()
                                 .stylist
                                 .style_for_anonymous_box(&PseudoElement::ServoTableWrapper,
-                                                         &table_style);
+                                                         &table_style, &self.style_context().default_computed_values);
         let wrapper_fragment =
             Fragment::from_opaque_node_and_style(node.opaque(),
                                                  PseudoElementType::Normal,
@@ -1123,7 +1123,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                                                              caption_side::T::top);
 
         if let ConstructionResult::Flow(table_flow, table_abs_descendants) = construction_result {
-            legalizer.add_child(&self.style_context().stylist, &mut wrapper_flow, table_flow);
+            legalizer.add_child(self.style_context(), &mut wrapper_flow, table_flow);
             abs_descendants.push_descendants(table_abs_descendants);
         }
 
@@ -1889,16 +1889,16 @@ impl Legalizer {
 
     /// Makes the `child` flow a new child of `parent`. Anonymous flows are automatically inserted
     /// to keep the tree legal.
-    fn add_child(&mut self, stylist: &Stylist, parent: &mut FlowRef, mut child: FlowRef) {
+    fn add_child(&mut self, context: &SharedStyleContext, parent: &mut FlowRef, mut child: FlowRef) {
         while !self.stack.is_empty() {
-            if self.try_to_add_child(stylist, parent, &mut child) {
+            if self.try_to_add_child(context, parent, &mut child) {
                 return
             }
             self.flush_top_of_stack(parent)
         }
 
-        while !self.try_to_add_child(stylist, parent, &mut child) {
-            self.push_next_anonymous_flow(stylist, parent)
+        while !self.try_to_add_child(context, parent, &mut child) {
+            self.push_next_anonymous_flow(context, parent)
         }
     }
 
@@ -1915,7 +1915,7 @@ impl Legalizer {
     /// This method attempts to create anonymous blocks in between `parent` and `child` if and only
     /// if those blocks will only ever have `child` as their sole child. At present, this is only
     /// true for anonymous block children of flex flows.
-    fn try_to_add_child(&mut self, stylist: &Stylist, parent: &mut FlowRef, child: &mut FlowRef)
+    fn try_to_add_child(&mut self, context: &SharedStyleContext, parent: &mut FlowRef, child: &mut FlowRef)
                         -> bool {
         let mut parent = self.stack.last_mut().unwrap_or(parent);
         let (parent_class, child_class) = (parent.class(), child.class());
@@ -1947,7 +1947,7 @@ impl Legalizer {
             (FlowClass::Flex, FlowClass::Inline) => {
                 flow::mut_base(FlowRef::deref_mut(child)).flags.insert(MARGINS_CANNOT_COLLAPSE);
                 let mut block_wrapper =
-                    Legalizer::create_anonymous_flow(stylist,
+                    Legalizer::create_anonymous_flow(context,
                                                      parent,
                                                      &[PseudoElement::ServoAnonymousBlock],
                                                      SpecificFragmentInfo::Generic,
@@ -1999,32 +1999,32 @@ impl Legalizer {
 
     /// Adds the anonymous flow that would be necessary to make an illegal child of `parent` legal
     /// to the stack.
-    fn push_next_anonymous_flow(&mut self, stylist: &Stylist, parent: &FlowRef) {
+    fn push_next_anonymous_flow(&mut self, context: &SharedStyleContext, parent: &FlowRef) {
         let parent_class = self.stack.last().unwrap_or(parent).class();
         match parent_class {
             FlowClass::TableRow => {
-                self.push_new_anonymous_flow(stylist,
+                self.push_new_anonymous_flow(context,
                                              parent,
                                              &[PseudoElement::ServoAnonymousTableCell],
                                              SpecificFragmentInfo::TableCell,
                                              TableCellFlow::from_fragment)
             }
             FlowClass::Table | FlowClass::TableRowGroup => {
-                self.push_new_anonymous_flow(stylist,
+                self.push_new_anonymous_flow(context,
                                              parent,
                                              &[PseudoElement::ServoAnonymousTableRow],
                                              SpecificFragmentInfo::TableRow,
                                              TableRowFlow::from_fragment)
             }
             FlowClass::TableWrapper => {
-                self.push_new_anonymous_flow(stylist,
+                self.push_new_anonymous_flow(context,
                                              parent,
                                              &[PseudoElement::ServoAnonymousTable],
                                              SpecificFragmentInfo::Table,
                                              TableFlow::from_fragment)
             }
             _ => {
-                self.push_new_anonymous_flow(stylist,
+                self.push_new_anonymous_flow(context,
                                              parent,
                                              &[PseudoElement::ServoTableWrapper,
                                                PseudoElement::ServoAnonymousTableWrapper],
@@ -2036,13 +2036,13 @@ impl Legalizer {
 
     /// Creates an anonymous flow and pushes it onto the stack.
     fn push_new_anonymous_flow<F>(&mut self,
-                                  stylist: &Stylist,
+                                  context: &SharedStyleContext,
                                   reference: &FlowRef,
                                   pseudos: &[PseudoElement],
                                   specific_fragment_info: SpecificFragmentInfo,
                                   constructor: extern "Rust" fn(Fragment) -> F)
                                   where F: Flow {
-        let new_flow = Legalizer::create_anonymous_flow(stylist,
+        let new_flow = Legalizer::create_anonymous_flow(context,
                                                         reference,
                                                         pseudos,
                                                         specific_fragment_info,
@@ -2055,7 +2055,7 @@ impl Legalizer {
     ///
     /// This method invokes the supplied constructor function on the given specific fragment info
     /// in order to actually generate the flow.
-    fn create_anonymous_flow<F>(stylist: &Stylist,
+    fn create_anonymous_flow<F>(context: &SharedStyleContext,
                                 reference: &FlowRef,
                                 pseudos: &[PseudoElement],
                                 specific_fragment_info: SpecificFragmentInfo,
@@ -2065,7 +2065,7 @@ impl Legalizer {
         let reference_block = reference.as_block();
         let mut new_style = reference_block.fragment.style.clone();
         for pseudo in pseudos {
-            new_style = stylist.style_for_anonymous_box(pseudo, &new_style)
+            new_style = context.stylist.style_for_anonymous_box(pseudo, &new_style, &context.default_computed_values)
         }
         let fragment = reference_block.fragment
                                       .create_similar_anonymous_fragment(new_style,
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 78a1295c1b5..4d25350835b 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -118,6 +118,7 @@ use style::error_reporting::{ParseErrorReporter, StdoutErrorReporter};
 use style::logical_geometry::LogicalPoint;
 use style::media_queries::{Device, MediaType};
 use style::parser::ParserContextExtraData;
+use style::properties::ComputedValues;
 use style::servo::restyle_damage::{REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, REPOSITION, STORE_OVERFLOW};
 use style::stylesheets::{Origin, Stylesheet, UserAgentStylesheets};
 use style::stylist::Stylist;
@@ -527,6 +528,11 @@ impl LayoutThread {
                 local_context_creation_data: Mutex::new(thread_local_style_context_creation_data),
                 timer: self.timer.clone(),
                 quirks_mode: self.quirks_mode.unwrap(),
+                // FIXME(bz): This isn't really right, but it's no more wrong
+                // than what we used to do.  See
+                // https://github.com/servo/servo/issues/14773 for fixing it
+                // properly.
+                default_computed_values: Arc::new(ComputedValues::initial_values().clone()),
             },
             image_cache_thread: Mutex::new(self.image_cache_thread.clone()),
             image_cache_sender: Mutex::new(self.image_cache_sender.clone()),
diff --git a/components/script_layout_interface/wrapper_traits.rs b/components/script_layout_interface/wrapper_traits.rs
index 77414fa48d5..0103b185096 100644
--- a/components/script_layout_interface/wrapper_traits.rs
+++ b/components/script_layout_interface/wrapper_traits.rs
@@ -391,6 +391,7 @@ pub trait ThreadSafeLayoutElement: Clone + Copy + Sized + Debug +
                                 context.stylist.precomputed_values_for_pseudo(
                                     &style_pseudo,
                                     Some(&data.styles().primary.values),
+                                    &context.default_computed_values,
                                     false);
                             data.styles_mut().pseudos
                                 .insert(style_pseudo.clone(), new_style.unwrap());
@@ -407,7 +408,8 @@ pub trait ThreadSafeLayoutElement: Clone + Copy + Sized + Debug +
                                        .lazily_compute_pseudo_element_style(
                                            self,
                                            &style_pseudo,
-                                           &data.styles().primary.values);
+                                           &data.styles().primary.values,
+                                           &context.default_computed_values);
                             data.styles_mut().pseudos
                                 .insert(style_pseudo.clone(), new_style.unwrap());
                         }
diff --git a/components/style/animation.rs b/components/style/animation.rs
index 2dabb608d99..1545cac72f8 100644
--- a/components/style/animation.rs
+++ b/components/style/animation.rs
@@ -430,6 +430,7 @@ fn compute_style_for_animation_step(context: &SharedStyleContext,
                                                /* is_root = */ false,
                                                iter,
                                                previous_style,
+                                               &context.default_computed_values,
                                                /* cascade_info = */ None,
                                                context.error_reporter.clone(),
                                                /* Metrics provider */ None,
diff --git a/components/style/build_gecko.rs b/components/style/build_gecko.rs
index 21f8b05dbf6..2eec1be1ce3 100644
--- a/components/style/build_gecko.rs
+++ b/components/style/build_gecko.rs
@@ -392,6 +392,7 @@ mod bindings {
                                         // for clang.
             "nsPIDOMWindow",  // <- Takes the vtable from a template parameter, and we can't
                               //    generate it conditionally.
+            "RawGeckoPresContext", // Just passing it through.
             "JS::Rooted",
             "mozilla::Maybe",
             "gfxSize",  // <- union { struct { T width; T height; }; T components[2] };
@@ -467,6 +468,7 @@ mod bindings {
             "RawGeckoDocument",
             "RawGeckoElement",
             "RawGeckoNode",
+            "RawGeckoPresContext",
             "ThreadSafeURIHolder",
             "ThreadSafePrincipalHolder",
             "ConsumeStyleBehavior",
@@ -560,6 +562,7 @@ mod bindings {
             "RawGeckoElement",
             "RawGeckoDocument",
             "RawServoDeclarationBlockStrong",
+            "RawGeckoPresContext",
         ];
         let servo_borrow_types = [
             "nsCSSValue",
diff --git a/components/style/context.rs b/components/style/context.rs
index 57a256d4911..ab5899e142f 100644
--- a/components/style/context.rs
+++ b/components/style/context.rs
@@ -13,6 +13,7 @@ use error_reporting::ParseErrorReporter;
 use euclid::Size2D;
 use matching::StyleSharingCandidateCache;
 use parking_lot::RwLock;
+use properties::ComputedValues;
 use std::collections::HashMap;
 use std::sync::{Arc, Mutex};
 use std::sync::mpsc::Sender;
@@ -82,6 +83,10 @@ pub struct SharedStyleContext {
 
     /// The QuirksMode state which the document needs to be rendered with
     pub quirks_mode: QuirksMode,
+
+    /// The default computed values to use for elements with no rules
+    /// applying to them.
+    pub default_computed_values: Arc<ComputedValues>,
 }
 
 /// A thread-local style context.
diff --git a/components/style/gecko/data.rs b/components/style/gecko/data.rs
index f67e3871bbc..dd4ae30a429 100644
--- a/components/style/gecko/data.rs
+++ b/components/style/gecko/data.rs
@@ -8,11 +8,13 @@ use animation::Animation;
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
 use dom::OpaqueNode;
 use euclid::size::TypedSize2D;
+use gecko_bindings::bindings::RawGeckoPresContextBorrowed;
 use gecko_bindings::bindings::RawServoStyleSet;
 use gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
 use media_queries::{Device, MediaType};
 use num_cpus;
 use parking_lot::RwLock;
+use properties::ComputedValues;
 use rayon;
 use std::cmp;
 use std::collections::HashMap;
@@ -55,6 +57,9 @@ pub struct PerDocumentStyleDataImpl {
 
     /// The number of threads of the work queue.
     pub num_threads: usize,
+
+    /// Default computed values for this document.
+    pub default_computed_values: Arc<ComputedValues>
 }
 
 /// The data itself is an `AtomicRefCell`, which guarantees the proper semantics
@@ -73,10 +78,15 @@ lazy_static! {
 
 impl PerDocumentStyleData {
     /// Create a dummy `PerDocumentStyleData`.
-    pub fn new() -> Self {
+    pub fn new(pres_context: RawGeckoPresContextBorrowed) -> Self {
         // FIXME(bholley): Real window size.
         let window_size: TypedSize2D<f32, ViewportPx> = TypedSize2D::new(800.0, 600.0);
-        let device = Device::new(MediaType::Screen, window_size);
+        let default_computed_values = ComputedValues::default_values(pres_context);
+
+        // FIXME(bz): We're going to need to either update the computed values
+        // in the Stylist's Device or give the Stylist a new Device when our
+        // default_computed_values changes.
+        let device = Device::new(MediaType::Screen, window_size, &default_computed_values);
 
         let (new_anims_sender, new_anims_receiver) = channel();
 
@@ -96,6 +106,7 @@ impl PerDocumentStyleData {
                 rayon::ThreadPool::new(configuration).ok()
             },
             num_threads: *NUM_THREADS,
+            default_computed_values: default_computed_values,
         }))
     }
 
diff --git a/components/style/gecko_bindings/bindings.rs b/components/style/gecko_bindings/bindings.rs
index 77a2fb2712d..1b560cd4518 100644
--- a/components/style/gecko_bindings/bindings.rs
+++ b/components/style/gecko_bindings/bindings.rs
@@ -6,6 +6,7 @@ type nsAString_internal = nsAString;
 use gecko_bindings::structs::RawGeckoDocument;
 use gecko_bindings::structs::RawGeckoElement;
 use gecko_bindings::structs::RawGeckoNode;
+use gecko_bindings::structs::RawGeckoPresContext;
 use gecko_bindings::structs::ThreadSafeURIHolder;
 use gecko_bindings::structs::ThreadSafePrincipalHolder;
 use gecko_bindings::structs::ConsumeStyleBehavior;
@@ -206,6 +207,8 @@ pub type RawGeckoDocumentBorrowed<'a> = &'a RawGeckoDocument;
 pub type RawGeckoDocumentBorrowedOrNull<'a> = Option<&'a RawGeckoDocument>;
 pub type RawServoDeclarationBlockStrongBorrowed<'a> = &'a RawServoDeclarationBlockStrong;
 pub type RawServoDeclarationBlockStrongBorrowedOrNull<'a> = Option<&'a RawServoDeclarationBlockStrong>;
+pub type RawGeckoPresContextBorrowed<'a> = &'a RawGeckoPresContext;
+pub type RawGeckoPresContextBorrowedOrNull<'a> = Option<&'a RawGeckoPresContext>;
 pub type nsCSSValueBorrowed<'a> = &'a nsCSSValue;
 pub type nsCSSValueBorrowedOrNull<'a> = Option<&'a nsCSSValue>;
 pub type nsCSSValueBorrowedMut<'a> = &'a mut nsCSSValue;
@@ -730,7 +733,9 @@ extern "C" {
                                                               *mut nsCSSValueSharedList);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleFont(ptr: *mut nsStyleFont);
+    pub fn Gecko_Construct_Default_nsStyleFont(ptr: *mut nsStyleFont,
+                                               pres_context:
+                                                   RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleFont(ptr: *mut nsStyleFont,
@@ -740,7 +745,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleFont(ptr: *mut nsStyleFont);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleColor(ptr: *mut nsStyleColor);
+    pub fn Gecko_Construct_Default_nsStyleColor(ptr: *mut nsStyleColor,
+                                                pres_context:
+                                                    RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleColor(ptr: *mut nsStyleColor,
@@ -750,7 +757,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleColor(ptr: *mut nsStyleColor);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleList(ptr: *mut nsStyleList);
+    pub fn Gecko_Construct_Default_nsStyleList(ptr: *mut nsStyleList,
+                                               pres_context:
+                                                   RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleList(ptr: *mut nsStyleList,
@@ -760,7 +769,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleList(ptr: *mut nsStyleList);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleText(ptr: *mut nsStyleText);
+    pub fn Gecko_Construct_Default_nsStyleText(ptr: *mut nsStyleText,
+                                               pres_context:
+                                                   RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleText(ptr: *mut nsStyleText,
@@ -770,7 +781,10 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleText(ptr: *mut nsStyleText);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleVisibility(ptr: *mut nsStyleVisibility);
+    pub fn Gecko_Construct_Default_nsStyleVisibility(ptr:
+                                                         *mut nsStyleVisibility,
+                                                     pres_context:
+                                                         RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleVisibility(ptr: *mut nsStyleVisibility,
@@ -781,8 +795,10 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleVisibility(ptr: *mut nsStyleVisibility);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleUserInterface(ptr:
-                                                    *mut nsStyleUserInterface);
+    pub fn Gecko_Construct_Default_nsStyleUserInterface(ptr:
+                                                            *mut nsStyleUserInterface,
+                                                        pres_context:
+                                                            RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleUserInterface(ptr:
@@ -794,7 +810,10 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleUserInterface(ptr: *mut nsStyleUserInterface);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleTableBorder(ptr: *mut nsStyleTableBorder);
+    pub fn Gecko_Construct_Default_nsStyleTableBorder(ptr:
+                                                          *mut nsStyleTableBorder,
+                                                      pres_context:
+                                                          RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleTableBorder(ptr:
@@ -806,7 +825,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleTableBorder(ptr: *mut nsStyleTableBorder);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleSVG(ptr: *mut nsStyleSVG);
+    pub fn Gecko_Construct_Default_nsStyleSVG(ptr: *mut nsStyleSVG,
+                                              pres_context:
+                                                  RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleSVG(ptr: *mut nsStyleSVG,
@@ -816,7 +837,10 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleSVG(ptr: *mut nsStyleSVG);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleVariables(ptr: *mut nsStyleVariables);
+    pub fn Gecko_Construct_Default_nsStyleVariables(ptr:
+                                                        *mut nsStyleVariables,
+                                                    pres_context:
+                                                        RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleVariables(ptr: *mut nsStyleVariables,
@@ -827,7 +851,10 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleVariables(ptr: *mut nsStyleVariables);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleBackground(ptr: *mut nsStyleBackground);
+    pub fn Gecko_Construct_Default_nsStyleBackground(ptr:
+                                                         *mut nsStyleBackground,
+                                                     pres_context:
+                                                         RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleBackground(ptr: *mut nsStyleBackground,
@@ -838,7 +865,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleBackground(ptr: *mut nsStyleBackground);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStylePosition(ptr: *mut nsStylePosition);
+    pub fn Gecko_Construct_Default_nsStylePosition(ptr: *mut nsStylePosition,
+                                                   pres_context:
+                                                       RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStylePosition(ptr: *mut nsStylePosition,
@@ -848,7 +877,10 @@ extern "C" {
     pub fn Gecko_Destroy_nsStylePosition(ptr: *mut nsStylePosition);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleTextReset(ptr: *mut nsStyleTextReset);
+    pub fn Gecko_Construct_Default_nsStyleTextReset(ptr:
+                                                        *mut nsStyleTextReset,
+                                                    pres_context:
+                                                        RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleTextReset(ptr: *mut nsStyleTextReset,
@@ -859,7 +891,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleTextReset(ptr: *mut nsStyleTextReset);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleDisplay(ptr: *mut nsStyleDisplay);
+    pub fn Gecko_Construct_Default_nsStyleDisplay(ptr: *mut nsStyleDisplay,
+                                                  pres_context:
+                                                      RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleDisplay(ptr: *mut nsStyleDisplay,
@@ -869,7 +903,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleDisplay(ptr: *mut nsStyleDisplay);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleContent(ptr: *mut nsStyleContent);
+    pub fn Gecko_Construct_Default_nsStyleContent(ptr: *mut nsStyleContent,
+                                                  pres_context:
+                                                      RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleContent(ptr: *mut nsStyleContent,
@@ -879,7 +915,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleContent(ptr: *mut nsStyleContent);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleUIReset(ptr: *mut nsStyleUIReset);
+    pub fn Gecko_Construct_Default_nsStyleUIReset(ptr: *mut nsStyleUIReset,
+                                                  pres_context:
+                                                      RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleUIReset(ptr: *mut nsStyleUIReset,
@@ -889,7 +927,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleUIReset(ptr: *mut nsStyleUIReset);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleTable(ptr: *mut nsStyleTable);
+    pub fn Gecko_Construct_Default_nsStyleTable(ptr: *mut nsStyleTable,
+                                                pres_context:
+                                                    RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleTable(ptr: *mut nsStyleTable,
@@ -899,7 +939,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleTable(ptr: *mut nsStyleTable);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleMargin(ptr: *mut nsStyleMargin);
+    pub fn Gecko_Construct_Default_nsStyleMargin(ptr: *mut nsStyleMargin,
+                                                 pres_context:
+                                                     RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleMargin(ptr: *mut nsStyleMargin,
@@ -909,7 +951,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleMargin(ptr: *mut nsStyleMargin);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStylePadding(ptr: *mut nsStylePadding);
+    pub fn Gecko_Construct_Default_nsStylePadding(ptr: *mut nsStylePadding,
+                                                  pres_context:
+                                                      RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStylePadding(ptr: *mut nsStylePadding,
@@ -919,7 +963,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStylePadding(ptr: *mut nsStylePadding);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleBorder(ptr: *mut nsStyleBorder);
+    pub fn Gecko_Construct_Default_nsStyleBorder(ptr: *mut nsStyleBorder,
+                                                 pres_context:
+                                                     RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleBorder(ptr: *mut nsStyleBorder,
@@ -929,7 +975,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleBorder(ptr: *mut nsStyleBorder);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleOutline(ptr: *mut nsStyleOutline);
+    pub fn Gecko_Construct_Default_nsStyleOutline(ptr: *mut nsStyleOutline,
+                                                  pres_context:
+                                                      RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleOutline(ptr: *mut nsStyleOutline,
@@ -939,7 +987,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleOutline(ptr: *mut nsStyleOutline);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleXUL(ptr: *mut nsStyleXUL);
+    pub fn Gecko_Construct_Default_nsStyleXUL(ptr: *mut nsStyleXUL,
+                                              pres_context:
+                                                  RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleXUL(ptr: *mut nsStyleXUL,
@@ -949,7 +999,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleXUL(ptr: *mut nsStyleXUL);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleSVGReset(ptr: *mut nsStyleSVGReset);
+    pub fn Gecko_Construct_Default_nsStyleSVGReset(ptr: *mut nsStyleSVGReset,
+                                                   pres_context:
+                                                       RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleSVGReset(ptr: *mut nsStyleSVGReset,
@@ -959,7 +1011,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleSVGReset(ptr: *mut nsStyleSVGReset);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleColumn(ptr: *mut nsStyleColumn);
+    pub fn Gecko_Construct_Default_nsStyleColumn(ptr: *mut nsStyleColumn,
+                                                 pres_context:
+                                                     RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleColumn(ptr: *mut nsStyleColumn,
@@ -969,7 +1023,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleColumn(ptr: *mut nsStyleColumn);
 }
 extern "C" {
-    pub fn Gecko_Construct_nsStyleEffects(ptr: *mut nsStyleEffects);
+    pub fn Gecko_Construct_Default_nsStyleEffects(ptr: *mut nsStyleEffects,
+                                                  pres_context:
+                                                      RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Gecko_CopyConstruct_nsStyleEffects(ptr: *mut nsStyleEffects,
@@ -979,6 +1035,9 @@ extern "C" {
     pub fn Gecko_Destroy_nsStyleEffects(ptr: *mut nsStyleEffects);
 }
 extern "C" {
+    pub fn Gecko_Construct_nsStyleVariables(ptr: *mut nsStyleVariables);
+}
+extern "C" {
     pub fn Servo_Element_ClearData(node: RawGeckoElementBorrowed);
 }
 extern "C" {
@@ -1028,7 +1087,14 @@ extern "C" {
      -> ServoCssRulesStrong;
 }
 extern "C" {
-    pub fn Servo_StyleSet_Init() -> RawServoStyleSetOwned;
+    pub fn Servo_StyleSet_Init(pres_context: RawGeckoPresContextBorrowed)
+     -> RawServoStyleSetOwned;
+}
+extern "C" {
+    pub fn Servo_StyleSet_RecomputeDefaultStyles(set:
+                                                     RawServoStyleSetBorrowed,
+                                                 pres_context:
+                                                     RawGeckoPresContextBorrowed);
 }
 extern "C" {
     pub fn Servo_StyleSet_AppendStyleSheet(set: RawServoStyleSetBorrowed,
@@ -1112,7 +1178,8 @@ extern "C" {
      -> RawServoDeclarationBlockStrong;
 }
 extern "C" {
-    pub fn Servo_RestyleWithAddedDeclaration(declarations:
+    pub fn Servo_RestyleWithAddedDeclaration(set: RawServoStyleSetBorrowed,
+                                             declarations:
                                                  RawServoDeclarationBlockBorrowed,
                                              previous_style:
                                                  ServoComputedValuesBorrowed)
@@ -1225,7 +1292,8 @@ extern "C" {
      -> ServoComputedValuesStrong;
 }
 extern "C" {
-    pub fn Servo_ComputedValues_Inherit(parent_style:
+    pub fn Servo_ComputedValues_Inherit(set: RawServoStyleSetBorrowed,
+                                        parent_style:
                                             ServoComputedValuesBorrowedOrNull)
      -> ServoComputedValuesStrong;
 }
@@ -1250,6 +1318,7 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_ResolveStyle(element: RawGeckoElementBorrowed,
+                              set: RawServoStyleSetBorrowed,
                               consume: ConsumeStyleBehavior)
      -> ServoComputedValuesStrong;
 }
diff --git a/components/style/gecko_bindings/structs_debug.rs b/components/style/gecko_bindings/structs_debug.rs
index 4f51b9b523a..25ed0cb366f 100644
--- a/components/style/gecko_bindings/structs_debug.rs
+++ b/components/style/gecko_bindings/structs_debug.rs
@@ -11613,12 +11613,14 @@ pub mod root {
     pub type RawGeckoNode = root::nsINode;
     pub type RawGeckoElement = root::mozilla::dom::Element;
     pub type RawGeckoDocument = root::nsIDocument;
+    pub type RawGeckoPresContext = [u64; 156usize];
     pub type RawGeckoNodeBorrowed = *const root::RawGeckoNode;
     pub type RawGeckoNodeBorrowedOrNull = *const root::RawGeckoNode;
     pub type RawGeckoElementBorrowed = *const root::RawGeckoElement;
     pub type RawGeckoElementBorrowedOrNull = *const root::RawGeckoElement;
     pub type RawGeckoDocumentBorrowed = *const root::RawGeckoDocument;
     pub type RawGeckoDocumentBorrowedOrNull = *const root::RawGeckoDocument;
+    pub type RawGeckoPresContextBorrowed = *const [u64; 156usize];
     #[repr(u32)]
     #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
     pub enum nsCSSTokenSerializationType {
diff --git a/components/style/gecko_bindings/structs_release.rs b/components/style/gecko_bindings/structs_release.rs
index 27501f88a86..99e02860158 100644
--- a/components/style/gecko_bindings/structs_release.rs
+++ b/components/style/gecko_bindings/structs_release.rs
@@ -11540,12 +11540,14 @@ pub mod root {
     pub type RawGeckoNode = root::nsINode;
     pub type RawGeckoElement = root::mozilla::dom::Element;
     pub type RawGeckoDocument = root::nsIDocument;
+    pub type RawGeckoPresContext = [u64; 152usize];
     pub type RawGeckoNodeBorrowed = *const root::RawGeckoNode;
     pub type RawGeckoNodeBorrowedOrNull = *const root::RawGeckoNode;
     pub type RawGeckoElementBorrowed = *const root::RawGeckoElement;
     pub type RawGeckoElementBorrowedOrNull = *const root::RawGeckoElement;
     pub type RawGeckoDocumentBorrowed = *const root::RawGeckoDocument;
     pub type RawGeckoDocumentBorrowedOrNull = *const root::RawGeckoDocument;
+    pub type RawGeckoPresContextBorrowed = *const [u64; 152usize];
     #[repr(u32)]
     #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
     pub enum nsCSSTokenSerializationType {
diff --git a/components/style/matching.rs b/components/style/matching.rs
index af8cd4bf627..f8d019ea775 100644
--- a/components/style/matching.rs
+++ b/components/style/matching.rs
@@ -470,6 +470,7 @@ trait PrivateMatchMethods: TElement {
                 cascade(shared_context.viewport_size,
                         rule_node,
                         Some(&***parent_style),
+                        &shared_context.default_computed_values,
                         Some(&mut cascade_info),
                         shared_context.error_reporter.clone(),
                         cascade_flags)
@@ -478,6 +479,7 @@ trait PrivateMatchMethods: TElement {
                 cascade(shared_context.viewport_size,
                         rule_node,
                         None,
+                        &shared_context.default_computed_values,
                         Some(&mut cascade_info),
                         shared_context.error_reporter.clone(),
                         cascade_flags)
diff --git a/components/style/media_queries.rs b/components/style/media_queries.rs
index 5762effb4c2..98c621ad89a 100644
--- a/components/style/media_queries.rs
+++ b/components/style/media_queries.rs
@@ -10,14 +10,16 @@ use Atom;
 use app_units::Au;
 use cssparser::{Delimiter, Parser, Token};
 use euclid::size::{Size2D, TypedSize2D};
+use properties::ComputedValues;
 use serialize_comma_separated_list;
 use std::ascii::AsciiExt;
 use std::fmt;
+#[cfg(feature = "gecko")]
+use std::sync::Arc;
 use style_traits::{ToCss, ViewportPx};
 use values::computed::{self, ToComputedValue};
 use values::specified;
 
-
 #[derive(Debug, PartialEq)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct MediaList {
@@ -47,10 +49,18 @@ pub enum Range<T> {
 }
 
 impl Range<specified::Length> {
-    fn to_computed_range(&self, viewport_size: Size2D<Au>) -> Range<Au> {
+    fn to_computed_range(&self, viewport_size: Size2D<Au>, default_values: &ComputedValues) -> Range<Au> {
         // http://dev.w3.org/csswg/mediaqueries3/#units
         // em units are relative to the initial font-size.
-        let context = computed::Context::initial(viewport_size, false);
+        let context = computed::Context {
+            is_root_element: false,
+            viewport_size: viewport_size,
+            inherited_style: default_values,
+            // This cloning business is kind of dumb.... It's because Context
+            // insists on having an actual ComputedValues inside itself.
+            style: default_values.clone(),
+            font_metrics_provider: None
+        };
 
         match *self {
             Range::Min(ref width) => Range::Min(width.to_computed_value(&context)),
@@ -225,9 +235,12 @@ impl MediaType {
 pub struct Device {
     pub media_type: MediaType,
     pub viewport_size: TypedSize2D<f32, ViewportPx>,
+    #[cfg(feature = "gecko")]
+    pub default_values: Arc<ComputedValues>,
 }
 
 impl Device {
+    #[cfg(feature = "servo")]
     pub fn new(media_type: MediaType, viewport_size: TypedSize2D<f32, ViewportPx>) -> Device {
         Device {
             media_type: media_type,
@@ -235,6 +248,26 @@ impl Device {
         }
     }
 
+    #[cfg(feature = "servo")]
+    pub fn default_values(&self) -> &ComputedValues {
+        ComputedValues::initial_values()
+    }
+
+    #[cfg(feature = "gecko")]
+    pub fn new(media_type: MediaType, viewport_size: TypedSize2D<f32, ViewportPx>,
+               default_values: &Arc<ComputedValues>) -> Device {
+        Device {
+            media_type: media_type,
+            viewport_size: viewport_size,
+            default_values: default_values.clone(),
+        }
+    }
+
+    #[cfg(feature = "gecko")]
+    pub fn default_values(&self) -> &ComputedValues {
+        &*self.default_values
+    }
+
     #[inline]
     pub fn au_viewport_size(&self) -> Size2D<Au> {
         Size2D::new(Au::from_f32_px(self.viewport_size.width),
@@ -337,7 +370,7 @@ impl MediaList {
             let query_match = media_match && mq.expressions.iter().all(|expression| {
                 match *expression {
                     Expression::Width(ref value) =>
-                        value.to_computed_range(viewport_size).evaluate(viewport_size.width),
+                        value.to_computed_range(viewport_size, device.default_values()).evaluate(viewport_size.width),
                 }
             });
 
diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index ab0f6b4d46c..2a6dde3e576 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -15,7 +15,7 @@ use custom_properties::ComputedValuesMap;
 use gecko_bindings::bindings;
 % for style_struct in data.style_structs:
 use gecko_bindings::structs::${style_struct.gecko_ffi_name};
-use gecko_bindings::bindings::Gecko_Construct_${style_struct.gecko_ffi_name};
+use gecko_bindings::bindings::Gecko_Construct_Default_${style_struct.gecko_ffi_name};
 use gecko_bindings::bindings::Gecko_CopyConstruct_${style_struct.gecko_ffi_name};
 use gecko_bindings::bindings::Gecko_Destroy_${style_struct.gecko_ffi_name};
 % endfor
@@ -40,6 +40,7 @@ use gecko_bindings::bindings::Gecko_SetMozBinding;
 use gecko_bindings::bindings::Gecko_SetNullImageValue;
 use gecko_bindings::bindings::ServoComputedValuesBorrowedOrNull;
 use gecko_bindings::bindings::{Gecko_ResetFilters, Gecko_CopyFiltersFrom};
+use gecko_bindings::bindings::RawGeckoPresContextBorrowed;
 use gecko_bindings::structs;
 use gecko_bindings::structs::nsStyleVariables;
 use gecko_bindings::sugar::ns_style_coord::{CoordDataValue, CoordData, CoordDataMut};
@@ -53,7 +54,6 @@ use properties::longhands;
 use std::fmt::{self, Debug};
 use std::mem::{transmute, zeroed};
 use std::ptr;
-use std::sync::atomic::{ATOMIC_USIZE_INIT, AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::cmp;
 
@@ -76,7 +76,7 @@ pub struct ComputedValues {
 }
 
 impl ComputedValues {
-    pub fn inherit_from(parent: &Arc<Self>) -> Arc<Self> {
+    pub fn inherit_from(parent: &Arc<Self>, default: &Arc<Self>) -> Arc<Self> {
         Arc::new(ComputedValues {
             custom_properties: parent.custom_properties.clone(),
             shareable: parent.shareable,
@@ -86,7 +86,7 @@ impl ComputedValues {
             % if style_struct.inherited:
             ${style_struct.ident}: parent.${style_struct.ident}.clone(),
             % else:
-            ${style_struct.ident}: Self::initial_values().${style_struct.ident}.clone(),
+            ${style_struct.ident}: default.${style_struct.ident}.clone(),
             % endif
             % endfor
         })
@@ -111,37 +111,16 @@ impl ComputedValues {
         }
     }
 
-    pub fn style_for_child_text_node(parent: &Arc<Self>) -> Arc<Self> {
-        // Gecko expects text nodes to be styled as if they were elements that
-        // matched no rules (that is, inherited style structs are inherited and
-        // non-inherited style structs are set to their initial values).
-        ComputedValues::inherit_from(parent)
-    }
-
-    pub fn initial_values() -> &'static Self {
-        unsafe {
-            debug_assert!(!raw_initial_values().is_null());
-            &*raw_initial_values()
-        }
-    }
-
-    pub unsafe fn initialize() {
-        debug_assert!(raw_initial_values().is_null());
-        set_raw_initial_values(Box::into_raw(Box::new(ComputedValues {
-            % for style_struct in data.style_structs:
-               ${style_struct.ident}: style_structs::${style_struct.name}::initial(),
-            % endfor
+    pub fn default_values(pres_context: RawGeckoPresContextBorrowed) -> Arc<Self> {
+        Arc::new(ComputedValues {
             custom_properties: None,
             shareable: true,
-            writing_mode: WritingMode::empty(),
-            root_font_size: longhands::font_size::get_initial_value(),
-        })));
-    }
-
-    pub unsafe fn shutdown() {
-        debug_assert!(!raw_initial_values().is_null());
-        let _ = Box::from_raw(raw_initial_values());
-        set_raw_initial_values(ptr::null_mut());
+            writing_mode: WritingMode::empty(), // FIXME(bz): This seems dubious
+            root_font_size: longhands::font_size::get_initial_value(), // FIXME(bz): Also seems dubious?
+            % for style_struct in data.style_structs:
+                ${style_struct.ident}: style_structs::${style_struct.name}::default(pres_context),
+            % endfor
+        })
     }
 
     % for style_struct in data.style_structs:
@@ -415,10 +394,11 @@ def set_gecko_property(ffi_name, expr):
 <%def name="impl_style_struct(style_struct)">
 impl ${style_struct.gecko_struct_name} {
     #[allow(dead_code, unused_variables)]
-    pub fn initial() -> Arc<Self> {
+    pub fn default(pres_context: RawGeckoPresContextBorrowed) -> Arc<Self> {
         let mut result = Arc::new(${style_struct.gecko_struct_name} { gecko: unsafe { zeroed() } });
         unsafe {
-            Gecko_Construct_${style_struct.gecko_ffi_name}(&mut Arc::get_mut(&mut result).unwrap().gecko);
+            Gecko_Construct_Default_${style_struct.gecko_ffi_name}(&mut Arc::get_mut(&mut result).unwrap().gecko,
+                                                                   pres_context);
         }
         result
     }
@@ -2646,13 +2626,3 @@ pub unsafe extern "C" fn Servo_GetStyleVariables(_cv: ServoComputedValuesBorrowe
     &*EMPTY_VARIABLES_STRUCT
 }
 
-// To avoid UB, we store the initial values as a atomic. It would be nice to
-// store them as AtomicPtr, but we can't have static AtomicPtr without const
-// fns, which aren't in stable Rust.
-static INITIAL_VALUES_STORAGE: AtomicUsize = ATOMIC_USIZE_INIT;
-unsafe fn raw_initial_values() -> *mut ComputedValues {
-    INITIAL_VALUES_STORAGE.load(Ordering::Relaxed) as *mut ComputedValues
-}
-unsafe fn set_raw_initial_values(v: *mut ComputedValues) {
-    INITIAL_VALUES_STORAGE.store(v as usize, Ordering::Relaxed);
-}
diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index 89e9d1d2b2e..f072da97c8f 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -210,6 +210,7 @@
         #[allow(unused_variables)]
         pub fn cascade_property(declaration: &PropertyDeclaration,
                                 inherited_style: &ComputedValues,
+                                default_style: &Arc<ComputedValues>,
                                 context: &mut computed::Context,
                                 seen: &mut PropertyBitField,
                                 cacheable: &mut bool,
@@ -260,7 +261,7 @@
                             DeclaredValue::Initial => {
                                 // We assume that it's faster to use copy_*_from rather than
                                 // set_*(get_initial_value());
-                                let initial_struct = ComputedValues::initial_values()
+                                let initial_struct = default_style
                                                       .get_${data.current_style_struct.name_lower}();
                                 context.mutate_style().mutate_${data.current_style_struct.name_lower}()
                                                       .copy_${property.ident}_from(initial_struct ${maybe_wm});
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 0a5eb2d3087..77175707ef2 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -1658,6 +1658,7 @@ mod lazy_static_module {
 pub type CascadePropertyFn =
     extern "Rust" fn(declaration: &PropertyDeclaration,
                      inherited_style: &ComputedValues,
+                     default_style: &Arc<ComputedValues>,
                      context: &mut computed::Context,
                      seen: &mut PropertyBitField,
                      cacheable: &mut bool,
@@ -1704,13 +1705,14 @@ bitflags! {
 pub fn cascade(viewport_size: Size2D<Au>,
                rule_node: &StrongRuleNode,
                parent_style: Option<<&ComputedValues>,
+               default_style: &Arc<ComputedValues>,
                cascade_info: Option<<&mut CascadeInfo>,
                error_reporter: StdBox<ParseErrorReporter + Send>,
                flags: CascadeFlags)
                -> ComputedValues {
     let (is_root_element, inherited_style) = match parent_style {
         Some(parent_style) => (false, parent_style),
-        None => (true, ComputedValues::initial_values()),
+        None => (true, &**default_style),
     };
     // Hold locks until after the apply_declarations() call returns.
     // Use filter_map because the root node has no style source.
@@ -1735,6 +1737,7 @@ pub fn cascade(viewport_size: Size2D<Au>,
                        is_root_element,
                        iter_declarations,
                        inherited_style,
+                       default_style,
                        cascade_info,
                        error_reporter,
                        None,
@@ -1747,6 +1750,7 @@ pub fn apply_declarations<'a, F, I>(viewport_size: Size2D<Au>,
                                     is_root_element: bool,
                                     iter_declarations: F,
                                     inherited_style: &ComputedValues,
+                                    default_style: &Arc<ComputedValues>,
                                     mut cascade_info: Option<<&mut CascadeInfo>,
                                     mut error_reporter: StdBox<ParseErrorReporter + Send>,
                                     font_metrics_provider: Option<<&FontMetricsProvider>,
@@ -1773,8 +1777,6 @@ pub fn apply_declarations<'a, F, I>(viewport_size: Size2D<Au>,
         ::custom_properties::finish_cascade(
             custom_properties, &inherited_custom_properties);
 
-    let initial_values = ComputedValues::initial_values();
-
     let starting_style = if !flags.contains(INHERIT_ALL) {
         ComputedValues::new(custom_properties,
                             flags.contains(SHAREABLE),
@@ -1784,7 +1786,7 @@ pub fn apply_declarations<'a, F, I>(viewport_size: Size2D<Au>,
                                 % if style_struct.inherited:
                                     inherited_style.clone_${style_struct.name_lower}(),
                                 % else:
-                                    initial_values.clone_${style_struct.name_lower}(),
+                                    default_style.clone_${style_struct.name_lower}(),
                                 % endif
                             % endfor
                             )
@@ -1864,6 +1866,7 @@ pub fn apply_declarations<'a, F, I>(viewport_size: Size2D<Au>,
             let discriminant = longhand_id as usize;
             (CASCADE_PROPERTY[discriminant])(declaration,
                                              inherited_style,
+                                             default_style,
                                              &mut context,
                                              &mut seen,
                                              &mut cacheable,
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 1a1dfabaf3d..5952e242cf1 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -11,7 +11,9 @@ use data::ComputedStyle;
 use dom::{PresentationalHintsSynthetizer, TElement};
 use error_reporting::StdoutErrorReporter;
 use keyframes::KeyframesAnimation;
-use media_queries::{Device, MediaType};
+use media_queries::Device;
+#[cfg(feature = "servo")]
+use media_queries::MediaType;
 use parking_lot::RwLock;
 use properties::{self, CascadeFlags, ComputedValues, INHERIT_ALL, Importance};
 use properties::{PropertyDeclaration, PropertyDeclarationBlock};
@@ -34,6 +36,7 @@ use std::slice;
 use std::sync::Arc;
 use style_traits::viewport::ViewportConstraints;
 use stylesheets::{CssRule, Origin, StyleRule, Stylesheet, UserAgentStylesheets};
+#[cfg(feature = "servo")]
 use viewport::{self, MaybeNew, ViewportRule};
 
 pub use ::fnv::FnvHashMap;
@@ -274,6 +277,7 @@ impl Stylist {
     pub fn precomputed_values_for_pseudo(&self,
                                          pseudo: &PseudoElement,
                                          parent: Option<&Arc<ComputedValues>>,
+                                         default: &Arc<ComputedValues>,
                                          inherit_all: bool)
                                          -> Option<ComputedStyle> {
         debug_assert!(SelectorImpl::pseudo_element_cascade_type(pseudo).is_precomputed());
@@ -293,6 +297,7 @@ impl Stylist {
                 properties::cascade(self.device.au_viewport_size(),
                                     &rule_node,
                                     parent.map(|p| &**p),
+                                    default,
                                     None,
                                     Box::new(StdoutErrorReporter),
                                     flags);
@@ -306,7 +311,8 @@ impl Stylist {
     #[cfg(feature = "servo")]
     pub fn style_for_anonymous_box(&self,
                                    pseudo: &PseudoElement,
-                                   parent_style: &Arc<ComputedValues>)
+                                   parent_style: &Arc<ComputedValues>,
+                                   default_style: &Arc<ComputedValues>)
                                    -> Arc<ComputedValues> {
         // For most (but not all) pseudo-elements, we inherit all values from the parent.
         let inherit_all = match *pseudo {
@@ -325,7 +331,7 @@ impl Stylist {
                 unreachable!("That pseudo doesn't represent an anonymous box!")
             }
         };
-        self.precomputed_values_for_pseudo(&pseudo, Some(parent_style), inherit_all)
+        self.precomputed_values_for_pseudo(&pseudo, Some(parent_style), default_style, inherit_all)
             .expect("style_for_anonymous_box(): No precomputed values for that pseudo!")
             .values
     }
@@ -340,7 +346,8 @@ impl Stylist {
     pub fn lazily_compute_pseudo_element_style<E>(&self,
                                                   element: &E,
                                                   pseudo: &PseudoElement,
-                                                  parent: &Arc<ComputedValues>)
+                                                  parent: &Arc<ComputedValues>,
+                                                  default: &Arc<ComputedValues>)
                                                   -> Option<ComputedStyle>
         where E: ElementExt +
                  fmt::Debug +
@@ -368,6 +375,7 @@ impl Stylist {
             properties::cascade(self.device.au_viewport_size(),
                                 &rule_node,
                                 Some(&**parent),
+                                default,
                                 None,
                                 Box::new(StdoutErrorReporter),
                                 CascadeFlags::empty());
@@ -380,6 +388,10 @@ impl Stylist {
     ///
     /// This means that we may need to rebuild style data even if the
     /// stylesheets haven't changed.
+    ///
+    /// Viewport_Constraints::maybe_new is servo-only (see the comment above it
+    /// explaining why), so we need to be servo-only too, since we call it.
+    #[cfg(feature = "servo")]
     pub fn set_device(&mut self, mut device: Device, stylesheets: &[Arc<Stylesheet>]) {
         let cascaded_rule = ViewportRule {
             declarations: viewport::Cascade::from_stylesheets(stylesheets, &device).finish(),
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 2f8ca20fd42..8c739e4c3d7 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -62,20 +62,6 @@ impl<'a> Context<'a> {
     pub fn style(&self) -> &ComputedValues { &self.style }
     /// A mutable reference to the current style.
     pub fn mutate_style(&mut self) -> &mut ComputedValues { &mut self.style }
-
-    /// Creates a dummy computed context for use in multiple places, like
-    /// evaluating media queries.
-    pub fn initial(viewport_size: Size2D<Au>, is_root_element: bool) -> Self {
-        let initial_style = ComputedValues::initial_values();
-        // FIXME: Enforce a font metrics provider.
-        Context {
-            is_root_element: is_root_element,
-            viewport_size: viewport_size,
-            inherited_style: initial_style,
-            style: initial_style.clone(),
-            font_metrics_provider: None,
-        }
-    }
 }
 
 /// A trait to represent the conversion between computed and specified values.
diff --git a/components/style/viewport.rs b/components/style/viewport.rs
index d8d45016b25..38ff5a6942d 100644
--- a/components/style/viewport.rs
+++ b/components/style/viewport.rs
@@ -9,13 +9,18 @@
 
 #![deny(missing_docs)]
 
+#[cfg(feature = "servo")]
 use app_units::Au;
 use cssparser::{AtRuleParser, DeclarationListParser, DeclarationParser, Parser, parse_important};
 use cssparser::ToCss as ParserToCss;
+#[cfg(feature = "servo")]
 use euclid::scale_factor::ScaleFactor;
-use euclid::size::{Size2D, TypedSize2D};
+#[cfg(feature = "servo")]
+use euclid::size::Size2D;
+use euclid::size::TypedSize2D;
 use media_queries::Device;
 use parser::{ParserContext, log_css_error};
+#[cfg(feature = "servo")]
 use properties::ComputedValues;
 use std::ascii::AsciiExt;
 use std::borrow::Cow;
@@ -25,6 +30,7 @@ use std::str::Chars;
 use style_traits::{ToCss, ViewportPx};
 use style_traits::viewport::{Orientation, UserZoom, ViewportConstraints, Zoom};
 use stylesheets::{Stylesheet, Origin};
+#[cfg(feature = "servo")]
 use values::computed::{Context, ToComputedValue};
 use values::specified::{Length, LengthOrPercentageOrAuto, ViewportPercentageLength};
 
@@ -605,6 +611,11 @@ pub trait MaybeNew {
                  -> Option<ViewportConstraints>;
 }
 
+/// MaybeNew for ViewportConstraints uses ComputedValues::initial_values which
+/// is servo-only (not present in gecko).  Once it has been changed to properly
+/// use per-document initial computed values, or not use the initial computed
+/// values at all, it can go back to being compiled unconditionally.
+#[cfg(feature = "servo")]
 impl MaybeNew for ViewportConstraints {
     fn maybe_new(initial_viewport: TypedSize2D<f32, ViewportPx>,
                  rule: &ViewportRule)
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 87ef1c87738..aeb1fe6484e 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -36,6 +36,7 @@ use style::gecko_bindings::bindings::{RawServoStyleSheetStrong, ServoComputedVal
 use style::gecko_bindings::bindings::{ServoCssRulesBorrowed, ServoCssRulesStrong};
 use style::gecko_bindings::bindings::{nsACString, nsAString};
 use style::gecko_bindings::bindings::RawGeckoElementBorrowed;
+use style::gecko_bindings::bindings::RawGeckoPresContextBorrowed;
 use style::gecko_bindings::bindings::RawServoImportRuleBorrowed;
 use style::gecko_bindings::bindings::ServoComputedValuesBorrowedOrNull;
 use style::gecko_bindings::bindings::nsTArrayBorrowed_uintptr_t;
@@ -81,17 +82,12 @@ pub extern "C" fn Servo_Initialize() -> () {
     // See https://doc.rust-lang.org/log/env_logger/index.html for instructions.
     env_logger::init().unwrap();
 
-    // Allocate our default computed values.
-    unsafe { ComputedValues::initialize(); }
-
     // Pretend that we're a Servo Layout thread, to make some assertions happy.
     thread_state::initialize(thread_state::LAYOUT);
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_Shutdown() -> () {
-    // Destroy our default computed values.
-    unsafe { ComputedValues::shutdown(); }
 }
 
 fn create_shared_context(per_doc_data: &PerDocumentStyleDataImpl) -> SharedStyleContext {
@@ -111,20 +107,12 @@ fn create_shared_context(per_doc_data: &PerDocumentStyleDataImpl) -> SharedStyle
         timer: Timer::new(),
         // FIXME Find the real QuirksMode information for this document
         quirks_mode: QuirksMode::NoQuirks,
+        default_computed_values: per_doc_data.default_computed_values.clone(),
     }
 }
 
 fn traverse_subtree(element: GeckoElement, raw_data: RawServoStyleSetBorrowed,
                     unstyled_children_only: bool) {
-    // Force the creation of our lazily-constructed initial computed values on
-    // the main thread, since it's not safe to call elsewhere.
-    //
-    // FIXME(bholley): this should move into Servo_Initialize as soon as we get
-    // rid of the HackilyFindSomeDeviceContext stuff that happens during
-    // initial_values computation, since that stuff needs to be called further
-    // along in startup than the sensible place to call Servo_Initialize.
-    ComputedValues::initial_values();
-
     // When new content is inserted in a display:none subtree, we will call into
     // servo to try to style it. Detect that here and bail out.
     if let Some(parent) = element.parent_element() {
@@ -168,7 +156,8 @@ pub extern "C" fn Servo_TraverseSubtree(root: RawGeckoElementBorrowed,
 }
 
 #[no_mangle]
-pub extern "C" fn Servo_RestyleWithAddedDeclaration(declarations: RawServoDeclarationBlockBorrowed,
+pub extern "C" fn Servo_RestyleWithAddedDeclaration(raw_data: RawServoStyleSetBorrowed,
+                                                    declarations: RawServoDeclarationBlockBorrowed,
                                                     previous_style: ServoComputedValuesBorrowed)
   -> ServoComputedValuesStrong
 {
@@ -181,11 +170,14 @@ pub extern "C" fn Servo_RestyleWithAddedDeclaration(declarations: RawServoDeclar
         guard.declarations.iter().rev().map(|&(ref decl, _importance)| decl)
     };
 
+    let data = PerDocumentStyleData::from_ffi(raw_data).borrow();
+
     // FIXME (bug 1303229): Use the actual viewport size here
     let computed = apply_declarations(Size2D::new(Au(0), Au(0)),
                                       /* is_root_element = */ false,
                                       declarations,
                                       previous_style,
+                                      &data.default_computed_values,
                                       None,
                                       Box::new(StdoutErrorReporter),
                                       None,
@@ -529,7 +521,8 @@ pub extern "C" fn Servo_ComputedValues_GetForAnonymousBox(parent_style_or_null:
 
 
     let maybe_parent = ComputedValues::arc_from_borrowed(&parent_style_or_null);
-    let new_computed = data.stylist.precomputed_values_for_pseudo(&pseudo, maybe_parent, false)
+    let new_computed = data.stylist.precomputed_values_for_pseudo(&pseudo, maybe_parent,
+                                                                  &data.default_computed_values, false)
                            .map(|styles| styles.values);
     new_computed.map_or(Strong::null(), |c| c.into_strong())
 }
@@ -542,6 +535,7 @@ pub extern "C" fn Servo_ResolvePseudoStyle(element: RawGeckoElementBorrowed,
 {
     let element = GeckoElement(element);
     let data = unsafe { element.ensure_data() }.borrow_mut();
+    let doc_data = PerDocumentStyleData::from_ffi(raw_data);
 
     // FIXME(bholley): Assert against this.
     if data.get_styles().is_none() {
@@ -549,11 +543,10 @@ pub extern "C" fn Servo_ResolvePseudoStyle(element: RawGeckoElementBorrowed,
         return if is_probe {
             Strong::null()
         } else {
-            Arc::new(ComputedValues::initial_values().clone()).into_strong()
+            doc_data.borrow().default_computed_values.clone().into_strong()
         };
     }
 
-    let doc_data = PerDocumentStyleData::from_ffi(raw_data);
     match get_pseudo_style(element, pseudo_tag, data.styles(), doc_data) {
         Some(values) => values.into_strong(),
         None if !is_probe => data.styles().primary.values.clone().into_strong(),
@@ -572,20 +565,23 @@ fn get_pseudo_style(element: GeckoElement, pseudo_tag: *mut nsIAtom,
         PseudoElementCascadeType::Lazy => {
             let d = doc_data.borrow_mut();
             let base = &styles.primary.values;
-            d.stylist.lazily_compute_pseudo_element_style(&element, &pseudo, base)
+            d.stylist.lazily_compute_pseudo_element_style(&element, &pseudo, base, &d.default_computed_values)
                      .map(|s| s.values.clone())
         },
     }
 }
 
 #[no_mangle]
-pub extern "C" fn Servo_ComputedValues_Inherit(parent_style: ServoComputedValuesBorrowedOrNull)
+pub extern "C" fn Servo_ComputedValues_Inherit(
+  raw_data: RawServoStyleSetBorrowed,
+  parent_style: ServoComputedValuesBorrowedOrNull)
      -> ServoComputedValuesStrong {
+    let data = PerDocumentStyleData::from_ffi(raw_data).borrow();
     let maybe_arc = ComputedValues::arc_from_borrowed(&parent_style);
     let style = if let Some(reference) = maybe_arc.as_ref() {
-        ComputedValues::inherit_from(reference)
+        ComputedValues::inherit_from(reference, &data.default_computed_values)
     } else {
-        Arc::new(ComputedValues::initial_values().clone())
+        data.default_computed_values.clone()
     };
     style.into_strong()
 }
@@ -601,12 +597,22 @@ pub extern "C" fn Servo_ComputedValues_Release(ptr: ServoComputedValuesBorrowed)
 }
 
 #[no_mangle]
-pub extern "C" fn Servo_StyleSet_Init() -> RawServoStyleSetOwned {
-    let data = Box::new(PerDocumentStyleData::new());
+pub extern "C" fn Servo_StyleSet_Init(pres_context: RawGeckoPresContextBorrowed)
+  -> RawServoStyleSetOwned {
+    let data = Box::new(PerDocumentStyleData::new(pres_context));
     data.into_ffi()
 }
 
 #[no_mangle]
+pub extern "C" fn Servo_StyleSet_RecomputeDefaultStyles(
+  raw_data: RawServoStyleSetBorrowed,
+  pres_context: RawGeckoPresContextBorrowed) {
+    let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
+    data.default_computed_values = ComputedValues::default_values(pres_context);
+    // FIXME(bz): We need to update our Stylist's Device's computed values, but how?
+}
+
+#[no_mangle]
 pub extern "C" fn Servo_StyleSet_Drop(data: RawServoStyleSetOwned) -> () {
     let _ = data.into_box::<PerDocumentStyleData>();
 }
@@ -928,6 +934,7 @@ pub extern "C" fn Servo_CheckChangeHint(element: RawGeckoElementBorrowed) -> nsC
 
 #[no_mangle]
 pub extern "C" fn Servo_ResolveStyle(element: RawGeckoElementBorrowed,
+                                     raw_data: RawServoStyleSetBorrowed,
                                      consume: structs::ConsumeStyleBehavior)
                                      -> ServoComputedValuesStrong
 {
@@ -935,10 +942,11 @@ pub extern "C" fn Servo_ResolveStyle(element: RawGeckoElementBorrowed,
     debug!("Servo_ResolveStyle: {:?}, consume={:?}", element, consume);
 
     let mut data = unsafe { element.ensure_data() }.borrow_mut();
+    let per_doc_data = PerDocumentStyleData::from_ffi(raw_data).borrow();
 
     if !data.has_current_styles() {
         error!("Resolving style on unstyled element with lazy computation forbidden.");
-        return Arc::new(ComputedValues::initial_values().clone()).into_strong();
+        return per_doc_data.default_computed_values.clone().into_strong();
     }
 
     let values = data.styles().primary.values.clone();
diff --git a/tests/unit/style/parsing/image.rs b/tests/unit/style/parsing/image.rs
index 96069dd83cc..cb4dfac001e 100644
--- a/tests/unit/style/parsing/image.rs
+++ b/tests/unit/style/parsing/image.rs
@@ -8,6 +8,7 @@ use euclid::size::Size2D;
 use media_queries::CSSErrorReporterTest;
 use std::f32::consts::PI;
 use style::parser::ParserContext;
+use style::properties::ComputedValues;
 use style::stylesheets::Origin;
 use style::values::computed;
 use style::values::computed::{Angle, Context, ToComputedValue};
@@ -43,7 +44,14 @@ fn test_linear_gradient() {
     // Note that Angle(PI) is correct for top-to-bottom rendering, whereas Angle(0) would render bottom-to-top.
     // ref: https://developer.mozilla.org/en-US/docs/Web/CSS/angle
     let container = Size2D::new(Au::default(), Au::default());
-    let specified_context = Context::initial(container, true);
+    let initial_style = ComputedValues::initial_values();
+    let specified_context = Context {
+        is_root_element: true,
+        viewport_size: container,
+        inherited_style: initial_style,
+        style: initial_style.clone(),
+        font_metrics_provider: None,
+    };
     assert_eq!(specified::AngleOrCorner::None.to_computed_value(&specified_context),
                computed::AngleOrCorner::Angle(Angle(PI)));
 }