Auto merge of #20657 - emilio:gecko-sync, r=emilio

style: Sync changes from mozilla-central.

See each individual commit from details.

14 files changed, 327 insertions, 96 deletions

diff --git a/components/layout_thread/dom_wrapper.rs b/components/layout_thread/dom_wrapper.rs
index 55bacd037cb..309ddaf7e93 100644
--- a/components/layout_thread/dom_wrapper.rs
+++ b/components/layout_thread/dom_wrapper.rs
@@ -397,6 +397,14 @@ impl<'le> TElement for ServoLayoutElement<'le> {
         unsafe { self.element.is_html_element() }
     }
 
+    fn is_mathml_element(&self) -> bool {
+        *self.element.namespace() == ns!(mathml)
+    }
+
+    fn is_svg_element(&self) -> bool {
+        *self.element.namespace() == ns!(svg)
+    }
+
     fn style_attribute(&self) -> Option<ArcBorrow<StyleLocked<PropertyDeclarationBlock>>> {
         unsafe {
             (*self.element.style_attribute()).as_ref().map(|x| x.borrow_arc())
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 01b9a13ba40..71df0e70356 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -135,7 +135,7 @@ use style::selector_parser::{RestyleDamage, Snapshot};
 use style::shared_lock::{SharedRwLock as StyleSharedRwLock, SharedRwLockReadGuard};
 use style::str::{split_html_space_chars, str_join};
 use style::stylesheet_set::DocumentStylesheetSet;
-use style::stylesheets::{Stylesheet, StylesheetContents, Origin, OriginSet};
+use style::stylesheets::{CssRule, Stylesheet, Origin, OriginSet};
 use task_source::TaskSource;
 use time;
 use timers::OneshotTimerCallback;
@@ -216,17 +216,25 @@ impl PartialEq for StyleSheetInDocument {
 }
 
 impl ::style::stylesheets::StylesheetInDocument for StyleSheetInDocument {
-    fn contents(&self, guard: &SharedRwLockReadGuard) -> &StylesheetContents {
-        self.sheet.contents(guard)
+    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin {
+        self.sheet.origin(guard)
     }
 
-    fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
-        self.sheet.media(guard)
+    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.sheet.quirks_mode(guard)
     }
 
     fn enabled(&self) -> bool {
         self.sheet.enabled()
     }
+
+    fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
+        self.sheet.media(guard)
+    }
+
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.sheet.rules(guard)
+    }
 }
 
 /// <https://dom.spec.whatwg.org/#document>
diff --git a/components/style/dom.rs b/components/style/dom.rs
index acc1c364ca8..bee4d88329e 100644
--- a/components/style/dom.rs
+++ b/components/style/dom.rs
@@ -434,6 +434,15 @@ pub trait TElement:
     /// Return whether this element is an element in the HTML namespace.
     fn is_html_element(&self) -> bool;
 
+    /// Return whether this element is an element in the MathML namespace.
+    fn is_mathml_element(&self) -> bool;
+
+    /// Return whether this element is an element in the SVG namespace.
+    fn is_svg_element(&self) -> bool;
+
+    /// Return whether this element is an element in the XUL namespace.
+    fn is_xul_element(&self) -> bool { false }
+
     /// Return the list of slotted nodes of this node.
     fn slotted_nodes(&self) -> &[Self::ConcreteNode] {
         &[]
diff --git a/components/style/gecko/data.rs b/components/style/gecko/data.rs
index 9c58a292dfc..331b07ea551 100644
--- a/components/style/gecko/data.rs
+++ b/components/style/gecko/data.rs
@@ -5,6 +5,7 @@
 //! Data needed to style a Gecko document.
 
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
+use context::QuirksMode;
 use dom::TElement;
 use gecko_bindings::bindings::{self, RawServoStyleSet};
 use gecko_bindings::structs::{self, RawGeckoPresContextOwned, ServoStyleSetSizes, ServoStyleSheet};
@@ -17,7 +18,7 @@ use properties::ComputedValues;
 use selector_parser::SnapshotMap;
 use servo_arc::Arc;
 use shared_lock::{Locked, SharedRwLockReadGuard, StylesheetGuards};
-use stylesheets::{StylesheetContents, StylesheetInDocument};
+use stylesheets::{CssRule, Origin, StylesheetContents, StylesheetInDocument};
 use stylist::Stylist;
 
 /// Little wrapper to a Gecko style sheet.
@@ -58,6 +59,16 @@ impl GeckoStyleSheet {
             &*(self.raw()._base.mInner as *const StyleSheetInfo as *const ServoStyleSheetInner)
         }
     }
+
+    /// Gets the StylesheetContents for this stylesheet.
+    pub fn contents(&self) -> &StylesheetContents {
+        debug_assert!(!self.inner().mContents.mRawPtr.is_null());
+        unsafe {
+            let contents =
+                (&**StylesheetContents::as_arc(&&*self.inner().mContents.mRawPtr)) as *const _;
+            &*contents
+        }
+    }
 }
 
 impl Drop for GeckoStyleSheet {
@@ -74,13 +85,12 @@ impl Clone for GeckoStyleSheet {
 }
 
 impl StylesheetInDocument for GeckoStyleSheet {
-    fn contents(&self, _: &SharedRwLockReadGuard) -> &StylesheetContents {
-        debug_assert!(!self.inner().mContents.mRawPtr.is_null());
-        unsafe {
-            let contents =
-                (&**StylesheetContents::as_arc(&&*self.inner().mContents.mRawPtr)) as *const _;
-            &*contents
-        }
+    fn origin(&self, _guard: &SharedRwLockReadGuard) -> Origin {
+        self.contents().origin
+    }
+
+    fn quirks_mode(&self, _guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.contents().quirks_mode
     }
 
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
@@ -103,6 +113,11 @@ impl StylesheetInDocument for GeckoStyleSheet {
     fn enabled(&self) -> bool {
         true
     }
+
+    #[inline]
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.contents().rules(guard)
+    }
 }
 
 /// The container for data that a Servo-backed Gecko document needs to style
diff --git a/components/style/gecko/generated/structs.rs b/components/style/gecko/generated/structs.rs
index 0cf29c89cd6..ebe6b79afbc 100644
--- a/components/style/gecko/generated/structs.rs
+++ b/components/style/gecko/generated/structs.rs
@@ -18478,7 +18478,7 @@ pub mod root {
         eCSSProperty_flex_grow = 105,
         eCSSProperty_flex_shrink = 106,
         eCSSProperty_flex_wrap = 107,
-        eCSSProperty_float_ = 108,
+        eCSSProperty_float = 108,
         eCSSProperty__moz_float_edge = 109,
         eCSSProperty_flood_color = 110,
         eCSSProperty_flood_opacity = 111,
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index 2764c7e73b3..c00a41049c2 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -674,11 +674,6 @@ impl<'le> GeckoElement<'le> {
     }
 
     #[inline]
-    fn is_xul_element(&self) -> bool {
-        self.namespace_id() == (structs::root::kNameSpaceID_XUL as i32)
-    }
-
-    #[inline]
     fn has_id(&self) -> bool {
         self.as_node()
             .get_bool_flag(nsINode_BooleanFlag::ElementHasID)
@@ -826,7 +821,7 @@ impl<'le> GeckoElement<'le> {
         match self.parent_element() {
             Some(e) => {
                 e.local_name() == &*local_name!("use") &&
-                    e.namespace() == &*ns!("http://www.w3.org/2000/svg")
+                e.is_svg_element()
             },
             None => false,
         }
@@ -1058,7 +1053,22 @@ impl<'le> TElement for GeckoElement<'le> {
 
     #[inline]
     fn is_html_element(&self) -> bool {
-        self.namespace_id() == (structs::root::kNameSpaceID_XHTML as i32)
+        self.namespace_id() == structs::kNameSpaceID_XHTML as i32
+    }
+
+    #[inline]
+    fn is_mathml_element(&self) -> bool {
+        self.namespace_id() == structs::kNameSpaceID_MathML as i32
+    }
+
+    #[inline]
+    fn is_svg_element(&self) -> bool {
+        self.namespace_id() == structs::kNameSpaceID_SVG as i32
+    }
+
+    #[inline]
+    fn is_xul_element(&self) -> bool {
+        self.namespace_id() == structs::root::kNameSpaceID_XUL as i32
     }
 
     /// Return the list of slotted nodes of this node.
diff --git a/components/style/properties/data.py b/components/style/properties/data.py
index b7da420dd9e..938b2c2c2bf 100644
--- a/components/style/properties/data.py
+++ b/components/style/properties/data.py
@@ -311,10 +311,7 @@ class Longhand(object):
         return "<{} as ToAnimatedValue>::AnimatedValue".format(computed)
 
     def nscsspropertyid(self):
-        ident = self.ident
-        if ident == "float":
-            ident = "float_"
-        return "nsCSSPropertyID::eCSSProperty_%s" % ident
+        return "nsCSSPropertyID::eCSSProperty_%s" % self.ident
 
 
 class Shorthand(object):
diff --git a/components/style/style_adjuster.rs b/components/style/style_adjuster.rs
index 10e62b87cc2..b7270976ead 100644
--- a/components/style/style_adjuster.rs
+++ b/components/style/style_adjuster.rs
@@ -23,6 +23,86 @@ pub struct StyleAdjuster<'a, 'b: 'a> {
     style: &'a mut StyleBuilder<'b>,
 }
 
+#[cfg(feature = "gecko")]
+fn is_topmost_svg_svg_element<E>(e: E) -> bool
+where
+    E: TElement,
+{
+    debug_assert!(e.is_svg_element());
+    if e.local_name() != &*atom!("svg") {
+        return false;
+    }
+
+    let parent = match e.traversal_parent() {
+        Some(n) => n,
+        None => return true,
+    };
+
+    if !parent.is_svg_element() {
+        return true;
+    }
+
+    parent.local_name() == &*atom!("foreignObject")
+}
+
+// https://drafts.csswg.org/css-display/#unbox
+#[cfg(feature = "gecko")]
+fn is_effective_display_none_for_display_contents<E>(element: E) -> bool
+where
+    E: TElement,
+{
+    use Atom;
+
+    // FIXME(emilio): This should be an actual static.
+    lazy_static! {
+        static ref SPECIAL_HTML_ELEMENTS: [Atom; 16] = [
+            atom!("br"), atom!("wbr"), atom!("meter"), atom!("progress"),
+            atom!("canvas"), atom!("embed"), atom!("object"), atom!("audio"),
+            atom!("iframe"), atom!("img"), atom!("video"), atom!("frame"),
+            atom!("frameset"), atom!("input"), atom!("textarea"),
+            atom!("select"),
+        ];
+    }
+
+    // https://drafts.csswg.org/css-display/#unbox-svg
+    //
+    // There's a note about "Unknown elements", but there's not a good way to
+    // know what that means, or to get that information from here, and no other
+    // UA implements this either.
+    lazy_static! {
+        static ref SPECIAL_SVG_ELEMENTS: [Atom; 6] = [
+            atom!("svg"), atom!("a"), atom!("g"), atom!("use"),
+            atom!("tspan"), atom!("textPath"),
+        ];
+    }
+
+    // https://drafts.csswg.org/css-display/#unbox-html
+    if element.is_html_element() {
+        let local_name = element.local_name();
+        return SPECIAL_HTML_ELEMENTS.iter().any(|name| &**name == local_name);
+    }
+
+    // https://drafts.csswg.org/css-display/#unbox-svg
+    if element.is_svg_element() {
+        if is_topmost_svg_svg_element(element) {
+            return true;
+        }
+        let local_name = element.local_name();
+        return !SPECIAL_SVG_ELEMENTS.iter().any(|name| &**name == local_name);
+    }
+
+    // https://drafts.csswg.org/css-display/#unbox-mathml
+    //
+    // We always treat XUL as display: none. We don't use display:
+    // contents in XUL anyway, so should be fine to be consistent with
+    // MathML unless there's a use case for it.
+    if element.is_mathml_element() || element.is_xul_element() {
+        return true;
+    }
+
+    false
+}
+
 impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
     /// Trivially constructs a new StyleAdjuster.
     #[inline]
@@ -377,20 +457,35 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
         }
     }
 
-    /// Native anonymous content converts display:contents into display:inline.
+    /// Handles the relevant sections in:
+    ///
+    /// https://drafts.csswg.org/css-display/#unbox-html
+    ///
+    /// And forbidding display: contents in pseudo-elements, at least for now.
     #[cfg(feature = "gecko")]
-    fn adjust_for_prohibited_display_contents(&mut self) {
-        // TODO: We should probably convert display:contents into display:none
-        // in some cases too: https://drafts.csswg.org/css-display/#unbox
-        //
+    fn adjust_for_prohibited_display_contents<E>(&mut self, element: Option<E>)
+    where
+        E: TElement,
+    {
+        if self.style.get_box().clone_display() != Display::Contents {
+            return;
+        }
+
         // FIXME(emilio): ::before and ::after should support display: contents,
         // see bug 1418138.
-        if self.style.pseudo.is_none() || self.style.get_box().clone_display() != Display::Contents
-        {
+        if self.style.pseudo.is_some() {
+            self.style.mutate_box().set_display(Display::Inline);
             return;
         }
 
-        self.style.mutate_box().set_display(Display::Inline);
+        let element = match element {
+            Some(e) => e,
+            None => return,
+        };
+
+        if is_effective_display_none_for_display_contents(element) {
+            self.style.mutate_box().set_display(Display::None);
+        }
     }
 
     /// If a <fieldset> has grid/flex display type, we need to inherit
@@ -657,7 +752,7 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
         self.adjust_for_visited(element);
         #[cfg(feature = "gecko")]
         {
-            self.adjust_for_prohibited_display_contents();
+            self.adjust_for_prohibited_display_contents(element);
             self.adjust_for_fieldset_content(layout_parent_style);
         }
         self.adjust_for_top_layer();
diff --git a/components/style/stylesheet_set.rs b/components/style/stylesheet_set.rs
index 1091b6674a1..a3b6e5cdc17 100644
--- a/components/style/stylesheet_set.rs
+++ b/components/style/stylesheet_set.rs
@@ -478,7 +478,7 @@ where
         sheet: &S,
         guard: &SharedRwLockReadGuard,
     ) -> &mut SheetCollection<S> {
-        let origin = sheet.contents(guard).origin;
+        let origin = sheet.origin(guard);
         self.collections.borrow_mut_for_origin(&origin)
     }
 
diff --git a/components/style/stylesheets/import_rule.rs b/components/style/stylesheets/import_rule.rs
index 75557ed50ee..fb50ec69732 100644
--- a/components/style/stylesheets/import_rule.rs
+++ b/components/style/stylesheets/import_rule.rs
@@ -6,6 +6,7 @@
 //!
 //! [import]: https://drafts.csswg.org/css-cascade-3/#at-import
 
+use context::QuirksMode;
 use cssparser::SourceLocation;
 use media_queries::MediaList;
 use shared_lock::{DeepCloneParams, DeepCloneWithLock};
@@ -13,13 +14,52 @@ use shared_lock::{SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt::{self, Write};
 use str::CssStringWriter;
 use style_traits::{CssWriter, ToCss};
-use stylesheets::{StylesheetContents, StylesheetInDocument};
+use stylesheets::{CssRule, Origin, StylesheetInDocument};
 use values::CssUrl;
 
+/// With asynchronous stylesheet parsing, we can't synchronously create a
+/// GeckoStyleSheet. So we use this placeholder instead.
+#[derive(Clone, Debug)]
+pub struct PendingSheet {
+    origin: Origin,
+    quirks_mode: QuirksMode,
+}
+
 /// A sheet that is held from an import rule.
 #[cfg(feature = "gecko")]
 #[derive(Debug)]
-pub struct ImportSheet(pub ::gecko::data::GeckoStyleSheet);
+pub enum ImportSheet {
+    /// A bonafide stylesheet.
+    Sheet(::gecko::data::GeckoStyleSheet),
+    /// An @import created while parsing off-main-thread, whose Gecko sheet has
+    /// yet to be created and attached.
+    Pending(PendingSheet),
+}
+
+#[cfg(feature = "gecko")]
+impl ImportSheet {
+    /// Creates a new ImportSheet from a GeckoStyleSheet.
+    pub fn new(sheet: ::gecko::data::GeckoStyleSheet) -> Self {
+        ImportSheet::Sheet(sheet)
+    }
+
+    /// Creates a pending ImportSheet for a load that has not started yet.
+    pub fn new_pending(origin: Origin, quirks_mode: QuirksMode) -> Self {
+        ImportSheet::Pending(PendingSheet {
+            origin,
+            quirks_mode,
+        })
+    }
+
+    /// Returns a reference to the GeckoStyleSheet in this ImportSheet, if it
+    /// exists.
+    pub fn as_sheet(&self) -> Option<&::gecko::data::GeckoStyleSheet> {
+        match *self {
+            ImportSheet::Sheet(ref s) => Some(s),
+            ImportSheet::Pending(_) => None,
+        }
+    }
+}
 
 #[cfg(feature = "gecko")]
 impl DeepCloneWithLock for ImportSheet {
@@ -31,10 +71,53 @@ impl DeepCloneWithLock for ImportSheet {
     ) -> Self {
         use gecko::data::GeckoStyleSheet;
         use gecko_bindings::bindings;
-        let clone = unsafe {
-            bindings::Gecko_StyleSheet_Clone(self.0.raw() as *const _, params.reference_sheet)
-        };
-        ImportSheet(unsafe { GeckoStyleSheet::from_addrefed(clone) })
+        match *self {
+            ImportSheet::Sheet(ref s) => {
+                let clone = unsafe {
+                    bindings::Gecko_StyleSheet_Clone(s.raw() as *const _, params.reference_sheet)
+                };
+                ImportSheet::Sheet(unsafe { GeckoStyleSheet::from_addrefed(clone) })
+            },
+            ImportSheet::Pending(ref p) => ImportSheet::Pending(p.clone()),
+        }
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl StylesheetInDocument for ImportSheet {
+    fn origin(&self, _guard: &SharedRwLockReadGuard) -> Origin {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.contents().origin,
+            ImportSheet::Pending(ref p) => p.origin,
+        }
+    }
+
+    fn quirks_mode(&self, _guard: &SharedRwLockReadGuard) -> QuirksMode {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.contents().quirks_mode,
+            ImportSheet::Pending(ref p) => p.quirks_mode,
+        }
+    }
+
+    fn enabled(&self) -> bool {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.enabled(),
+            ImportSheet::Pending(_) => true,
+        }
+    }
+
+    fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.media(guard),
+            ImportSheet::Pending(_) => None,
+        }
+    }
+
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.contents().rules(guard),
+            ImportSheet::Pending(_) => &[],
+        }
     }
 }
 
@@ -43,19 +126,27 @@ impl DeepCloneWithLock for ImportSheet {
 #[derive(Debug)]
 pub struct ImportSheet(pub ::servo_arc::Arc<::stylesheets::Stylesheet>);
 
+#[cfg(feature = "servo")]
 impl StylesheetInDocument for ImportSheet {
-    /// Get the media associated with this stylesheet.
-    fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
-        self.0.media(guard)
+    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin {
+        self.0.origin(guard)
     }
 
-    fn contents(&self, guard: &SharedRwLockReadGuard) -> &StylesheetContents {
-        self.0.contents(guard)
+    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.0.quirks_mode(guard)
     }
 
     fn enabled(&self) -> bool {
         self.0.enabled()
     }
+
+    fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
+        self.0.media(guard)
+    }
+
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.0.rules(guard)
+    }
 }
 
 #[cfg(feature = "servo")]
diff --git a/components/style/stylesheets/rules_iterator.rs b/components/style/stylesheets/rules_iterator.rs
index 3d63a218ff4..b46e24c22c7 100644
--- a/components/style/stylesheets/rules_iterator.rs
+++ b/components/style/stylesheets/rules_iterator.rs
@@ -9,7 +9,7 @@ use media_queries::Device;
 use shared_lock::SharedRwLockReadGuard;
 use smallvec::SmallVec;
 use std::slice;
-use stylesheets::{CssRule, CssRules, DocumentRule, ImportRule, MediaRule, SupportsRule};
+use stylesheets::{CssRule, DocumentRule, ImportRule, MediaRule, SupportsRule};
 use stylesheets::StylesheetInDocument;
 
 /// An iterator over a list of rules.
@@ -35,10 +35,10 @@ where
         device: &'a Device,
         quirks_mode: QuirksMode,
         guard: &'a SharedRwLockReadGuard<'b>,
-        rules: &'a CssRules,
+        rules: &'a [CssRule],
     ) -> Self {
         let mut stack = SmallVec::new();
-        stack.push(rules.0.iter());
+        stack.push(rules.iter());
         Self {
             device: device,
             quirks_mode: quirks_mode,
@@ -102,10 +102,7 @@ where
                         }
                         import_rule
                             .stylesheet
-                            .contents(self.guard)
-                            .rules
-                            .read_with(self.guard)
-                            .0
+                            .rules(self.guard)
                             .iter()
                     },
                     CssRule::Document(ref doc_rule) => {
diff --git a/components/style/stylesheets/stylesheet.rs b/components/style/stylesheets/stylesheet.rs
index 4bccbb504c9..08c2cb05f7a 100644
--- a/components/style/stylesheets/stylesheet.rs
+++ b/components/style/stylesheets/stylesheet.rs
@@ -103,22 +103,10 @@ impl StylesheetContents {
         }
     }
 
-    /// Return an iterator using the condition `C`.
+    /// Returns a reference to the list of rules.
     #[inline]
-    pub fn iter_rules<'a, 'b, C>(
-        &'a self,
-        device: &'a Device,
-        guard: &'a SharedRwLockReadGuard<'b>,
-    ) -> RulesIterator<'a, 'b, C>
-    where
-        C: NestedRuleIterationCondition,
-    {
-        RulesIterator::new(
-            device,
-            self.quirks_mode,
-            guard,
-            &self.rules.read_with(guard),
-        )
+    pub fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        &self.rules.read_with(guard).0
     }
 
     /// Measure heap usage.
@@ -189,32 +177,20 @@ macro_rules! rule_filter {
 
 /// A trait to represent a given stylesheet in a document.
 pub trait StylesheetInDocument {
-    /// Get the contents of this stylesheet.
-    fn contents(&self, guard: &SharedRwLockReadGuard) -> &StylesheetContents;
-
     /// Get the stylesheet origin.
-    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin {
-        self.contents(guard).origin
-    }
+    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin;
 
     /// Get the stylesheet quirks mode.
-    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode {
-        self.contents(guard).quirks_mode
-    }
+    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode;
+
+    /// Get whether this stylesheet is enabled.
+    fn enabled(&self) -> bool;
 
     /// Get the media associated with this stylesheet.
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList>;
 
-    /// Returns whether the style-sheet applies for the current device.
-    fn is_effective_for_device(&self, device: &Device, guard: &SharedRwLockReadGuard) -> bool {
-        match self.media(guard) {
-            Some(medialist) => medialist.evaluate(device, self.quirks_mode(guard)),
-            None => true,
-        }
-    }
-
-    /// Get whether this stylesheet is enabled.
-    fn enabled(&self) -> bool;
+    /// Returns a reference to the list of rules in this stylesheet.
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule];
 
     /// Return an iterator using the condition `C`.
     #[inline]
@@ -226,7 +202,15 @@ pub trait StylesheetInDocument {
     where
         C: NestedRuleIterationCondition,
     {
-        self.contents(guard).iter_rules(device, guard)
+        RulesIterator::new(device, self.quirks_mode(guard), guard, self.rules(guard))
+    }
+
+    /// Returns whether the style-sheet applies for the current device.
+    fn is_effective_for_device(&self, device: &Device, guard: &SharedRwLockReadGuard) -> bool {
+        match self.media(guard) {
+            Some(medialist) => medialist.evaluate(device, self.quirks_mode(guard)),
+            None => true,
+        }
     }
 
     /// Return an iterator over the effective rules within the style-sheet, as
@@ -255,8 +239,12 @@ pub trait StylesheetInDocument {
 }
 
 impl StylesheetInDocument for Stylesheet {
-    fn contents(&self, _: &SharedRwLockReadGuard) -> &StylesheetContents {
-        &self.contents
+    fn origin(&self, _guard: &SharedRwLockReadGuard) -> Origin {
+        self.contents.origin
+    }
+
+    fn quirks_mode(&self, _guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.contents.quirks_mode
     }
 
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
@@ -266,6 +254,11 @@ impl StylesheetInDocument for Stylesheet {
     fn enabled(&self) -> bool {
         !self.disabled()
     }
+
+    #[inline]
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.contents.rules(guard)
+    }
 }
 
 /// A simple wrapper over an `Arc<Stylesheet>`, with pointer comparison, and
@@ -289,8 +282,12 @@ impl ToMediaListKey for DocumentStyleSheet {
 }
 
 impl StylesheetInDocument for DocumentStyleSheet {
-    fn contents(&self, guard: &SharedRwLockReadGuard) -> &StylesheetContents {
-        self.0.contents(guard)
+    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin {
+        self.0.origin(guard)
+    }
+
+    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.0.quirks_mode(guard)
     }
 
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
@@ -300,6 +297,11 @@ impl StylesheetInDocument for DocumentStyleSheet {
     fn enabled(&self) -> bool {
         self.0.enabled()
     }
+
+    #[inline]
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.0.rules(guard)
+    }
 }
 
 impl Stylesheet {
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index ce957398391..3a476640de1 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -2048,7 +2048,7 @@ pub extern "C" fn Servo_ImportRule_GetSheet(
     rule: RawServoImportRuleBorrowed,
 ) -> *const ServoStyleSheet {
     read_locked_arc(rule, |rule: &ImportRule| {
-        rule.stylesheet.0.raw() as *const ServoStyleSheet
+        rule.stylesheet.as_sheet().unwrap().raw() as *const ServoStyleSheet
     })
 }
 
diff --git a/ports/geckolib/stylesheet_loader.rs b/ports/geckolib/stylesheet_loader.rs
index 0addb4f9ef8..1dfe30e8bdb 100644
--- a/ports/geckolib/stylesheet_loader.rs
+++ b/ports/geckolib/stylesheet_loader.rs
@@ -55,9 +55,8 @@ impl StyleStylesheetLoader for StylesheetLoader {
 
         debug_assert!(!child_sheet.is_null(),
                       "Import rules should always have a strong sheet");
-        let stylesheet = unsafe {
-            ImportSheet(GeckoStyleSheet::from_addrefed(child_sheet))
-        };
+        let sheet = unsafe { GeckoStyleSheet::from_addrefed(child_sheet) };
+        let stylesheet = ImportSheet::new(sheet);
         Arc::new(lock.wrap(ImportRule { url, source_location, stylesheet }))
     }
 }