Revert "Auto merge of #24677 - jdm:iframe-sizing-cleanup, r=asajeffrey"jdm-revert4

This reverts commit 9a518cf7979b79b34611135d09c1dd0a96945255, reversing
changes made to a33d493a4ff6f8a629a9b82202c49c41ecbefa49.

18 files changed, 150 insertions, 163 deletions

diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index 3df7e1a8a0c..94f578d48f1 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -209,6 +209,9 @@ pub struct IOCompositor<Window: WindowMethods + ?Sized> {
 
     /// True to translate mouse input into touch events.
     convert_mouse_to_touch: bool,
+
+    /// Ratio of device pixels per px at the default scale.
+    device_pixels_per_px: Option<f32>,
 }
 
 #[derive(Clone, Copy)]
@@ -281,6 +284,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         is_running_problem_test: bool,
         exit_after_load: bool,
         convert_mouse_to_touch: bool,
+        device_pixels_per_px: Option<f32>,
     ) -> Self {
         let composite_target = match output_file {
             Some(_) => CompositeTarget::PngFile,
@@ -323,6 +327,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
             is_running_problem_test,
             exit_after_load,
             convert_mouse_to_touch,
+            device_pixels_per_px,
         }
     }
 
@@ -333,6 +338,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         is_running_problem_test: bool,
         exit_after_load: bool,
         convert_mouse_to_touch: bool,
+        device_pixels_per_px: Option<f32>,
     ) -> Self {
         let mut compositor = IOCompositor::new(
             window,
@@ -341,11 +347,15 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
             is_running_problem_test,
             exit_after_load,
             convert_mouse_to_touch,
+            device_pixels_per_px,
         );
 
         // Set the size of the root layer.
         compositor.update_zoom_transform();
 
+        // Tell the constellation about the initial window size.
+        compositor.send_window_size(WindowSizeType::Initial);
+
         compositor
     }
 
@@ -635,6 +645,8 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
 
         self.create_pipeline_details_for_frame_tree(&frame_tree);
 
+        self.send_window_size(WindowSizeType::Initial);
+
         self.frame_tree_id.next();
     }
 
@@ -1069,10 +1081,13 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
     }
 
     fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
-        if self.output_file.is_some() {
-            return Scale::new(1.0);
+        match self.device_pixels_per_px {
+            Some(device_pixels_per_px) => Scale::new(device_pixels_per_px),
+            None => match self.output_file {
+                Some(_) => Scale::new(1.0),
+                None => self.embedder_coordinates.hidpi_factor,
+            },
         }
-        self.embedder_coordinates.hidpi_factor
     }
 
     fn device_pixels_per_page_px(&self) -> Scale<f32, CSSPixel, DevicePixel> {
diff --git a/components/constellation/constellation.rs b/components/constellation/constellation.rs
index 807495ff3f1..685f620f6b5 100644
--- a/components/constellation/constellation.rs
+++ b/components/constellation/constellation.rs
@@ -112,7 +112,7 @@ use compositing::SendableFrameTree;
 use crossbeam_channel::{after, never, unbounded, Receiver, Sender};
 use devtools_traits::{ChromeToDevtoolsControlMsg, DevtoolsControlMsg};
 use embedder_traits::{Cursor, EmbedderMsg, EmbedderProxy, EventLoopWaker};
-use euclid::{default::Size2D as UntypedSize2D, Size2D};
+use euclid::{default::Size2D as UntypedSize2D, Scale, Size2D};
 use gfx::font_cache_thread::FontCacheThread;
 use gfx_traits::Epoch;
 use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
@@ -157,6 +157,7 @@ use script_traits::{MessagePortMsg, PortMessageTask, StructuredSerializedData};
 use script_traits::{SWManagerMsg, ScopeThings, UpdatePipelineIdReason, WebDriverCommandMsg};
 use serde::{Deserialize, Serialize};
 use servo_config::{opts, pref};
+use servo_geometry::DeviceIndependentPixel;
 use servo_rand::{random, Rng, ServoRng, SliceRandom};
 use servo_remutex::ReentrantMutex;
 use servo_url::{Host, ImmutableOrigin, ServoUrl};
@@ -462,6 +463,10 @@ pub struct Constellation<Message, LTF, STF> {
 
     /// Mechanism to force the compositor to process events.
     event_loop_waker: Option<Box<dyn EventLoopWaker>>,
+
+    /// The ratio of device pixels per px at the default scale. If unspecified, will use the
+    /// platform default setting.
+    device_pixels_per_px: Option<f32>,
 }
 
 /// State needed to construct a constellation.
@@ -518,6 +523,10 @@ pub struct InitialConstellationState {
 
     /// Mechanism to force the compositor to process events.
     pub event_loop_waker: Option<Box<dyn EventLoopWaker>>,
+
+    /// The ratio of device pixels per px at the default scale. If unspecified, will use the
+    /// platform default setting.
+    pub device_pixels_per_px: Option<f32>,
 }
 
 /// Data needed for webdriver
@@ -693,7 +702,8 @@ where
     /// Create a new constellation thread.
     pub fn start(
         state: InitialConstellationState,
-        initial_window_size: WindowSizeData,
+        initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+        device_pixels_per_px: Option<f32>,
         random_pipeline_closure_probability: Option<f32>,
         random_pipeline_closure_seed: Option<usize>,
         is_running_problem_test: bool,
@@ -801,7 +811,10 @@ where
                     next_pipeline_namespace_id: PipelineNamespaceId(2),
                     time_profiler_chan: state.time_profiler_chan,
                     mem_profiler_chan: state.mem_profiler_chan,
-                    window_size: initial_window_size,
+                    window_size: WindowSizeData {
+                        initial_viewport: initial_window_size.to_f32() * Scale::new(1.0),
+                        device_pixel_ratio: Scale::new(device_pixels_per_px.unwrap_or(1.0)),
+                    },
                     phantom: PhantomData,
                     webdriver: WebDriverData::new(),
                     timer_scheduler: TimerScheduler::new(),
@@ -831,6 +844,7 @@ where
                     glplayer_threads: state.glplayer_threads,
                     player_context: state.player_context,
                     event_loop_waker: state.event_loop_waker,
+                    device_pixels_per_px,
                 };
 
                 constellation.run();
@@ -1060,12 +1074,10 @@ where
             resource_threads,
             time_profiler_chan: self.time_profiler_chan.clone(),
             mem_profiler_chan: self.mem_profiler_chan.clone(),
-            window_size: WindowSizeData {
-                initial_viewport: initial_window_size,
-                device_pixel_ratio: self.window_size.device_pixel_ratio,
-            },
+            window_size: initial_window_size,
             event_loop,
             load_data,
+            device_pixel_ratio: self.window_size.device_pixel_ratio,
             prev_visibility: is_visible,
             webrender_api_sender: self.webrender_api_sender.clone(),
             webrender_document: self.webrender_document,
@@ -1077,6 +1089,7 @@ where
             webxr_registry: self.webxr_registry.clone(),
             player_context: self.player_context.clone(),
             event_loop_waker: self.event_loop_waker.as_ref().map(|w| (*w).clone_box()),
+            device_pixels_per_px: self.device_pixels_per_px,
         });
 
         let pipeline = match result {
@@ -2216,7 +2229,6 @@ where
             new_pipeline_id: new_pipeline_id,
             replace: None,
             new_browsing_context_info: None,
-            window_size,
         });
     }
 
@@ -2361,7 +2373,6 @@ where
                 is_private: is_private,
                 is_visible: is_visible,
             }),
-            window_size,
         });
     }
 
@@ -2533,10 +2544,6 @@ where
         // https://github.com/rust-lang/rust/issues/59159
         let browsing_context_size = browsing_context.size;
         let browsing_context_is_visible = browsing_context.is_visible;
-        debug_assert_eq!(
-            browsing_context_size,
-            load_info.window_size.initial_viewport
-        );
 
         // Create the new pipeline, attached to the parent and push to pending changes
         self.new_pipeline(
@@ -2558,7 +2565,6 @@ where
             replace: replace,
             // Browsing context for iframe already exists.
             new_browsing_context_info: None,
-            window_size: load_info.window_size.initial_viewport,
         });
     }
 
@@ -2617,7 +2623,6 @@ where
                 is_private: is_private,
                 is_visible: is_parent_visible,
             }),
-            window_size: load_info.window_size.initial_viewport,
         });
     }
 
@@ -2706,7 +2711,6 @@ where
                 is_private: is_opener_private,
                 is_visible: is_opener_visible,
             }),
-            window_size: self.window_size.initial_viewport,
         });
     }
 
@@ -2910,7 +2914,6 @@ where
                     replace,
                     // `load_url` is always invoked on an existing browsing context.
                     new_browsing_context_info: None,
-                    window_size,
                 });
                 Some(new_pipeline_id)
             },
@@ -3230,7 +3233,6 @@ where
                     replace: Some(NeedsToReload::Yes(pipeline_id, load_data)),
                     // Browsing context must exist at this point.
                     new_browsing_context_info: None,
-                    window_size,
                 });
                 return;
             },
@@ -3988,7 +3990,7 @@ where
                     change.top_level_browsing_context_id,
                     change.new_pipeline_id,
                     new_context_info.parent_pipeline_id,
-                    change.window_size,
+                    self.window_size.initial_viewport, //XXXjdm is this valid?
                     new_context_info.is_private,
                     new_context_info.is_visible,
                 );
diff --git a/components/constellation/pipeline.rs b/components/constellation/pipeline.rs
index 3ac5ded15ed..2579343f3fe 100644
--- a/components/constellation/pipeline.rs
+++ b/components/constellation/pipeline.rs
@@ -12,6 +12,7 @@ use compositing::CompositorProxy;
 use crossbeam_channel::{unbounded, Sender};
 use devtools_traits::{DevtoolsControlMsg, ScriptToDevtoolsControlMsg};
 use embedder_traits::EventLoopWaker;
+use euclid::{Scale, Size2D};
 use gfx::font_cache_thread::FontCacheThread;
 use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
 use ipc_channel::router::ROUTER;
@@ -46,6 +47,8 @@ use std::process;
 use std::rc::Rc;
 use std::sync::atomic::AtomicBool;
 use std::sync::Arc;
+use style_traits::CSSPixel;
+use style_traits::DevicePixel;
 use webvr_traits::WebVRMsg;
 
 /// A `Pipeline` is the constellation's view of a `Document`. Each pipeline has an
@@ -162,7 +165,10 @@ pub struct InitialPipelineState {
     pub mem_profiler_chan: profile_mem::ProfilerChan,
 
     /// Information about the initial window size.
-    pub window_size: WindowSizeData,
+    pub window_size: Size2D<f32, CSSPixel>,
+
+    /// Information about the device pixel ratio.
+    pub device_pixel_ratio: Scale<f32, CSSPixel, DevicePixel>,
 
     /// The ID of the pipeline namespace for this script thread.
     pub pipeline_namespace_id: PipelineNamespaceId,
@@ -199,6 +205,10 @@ pub struct InitialPipelineState {
 
     /// Mechanism to force the compositor to process events.
     pub event_loop_waker: Option<Box<dyn EventLoopWaker>>,
+
+    /// The ratio of device pixels per px at the default scale. If unspecified, will use the
+    /// platform default setting.
+    pub device_pixels_per_px: Option<f32>,
 }
 
 pub struct NewPipeline {
@@ -218,6 +228,11 @@ impl Pipeline {
         // probably requires a general low-memory strategy.
         let (pipeline_chan, pipeline_port) = ipc::channel().expect("Pipeline main chan");
 
+        let window_size = WindowSizeData {
+            initial_viewport: state.window_size,
+            device_pixel_ratio: state.device_pixel_ratio,
+        };
+
         let (script_chan, sampler_chan) = match state.event_loop {
             Some(script_chan) => {
                 let new_layout_info = NewLayoutInfo {
@@ -227,7 +242,7 @@ impl Pipeline {
                     top_level_browsing_context_id: state.top_level_browsing_context_id,
                     opener: state.opener,
                     load_data: state.load_data.clone(),
-                    window_size: state.window_size,
+                    window_size: window_size,
                     pipeline_port: pipeline_port,
                 };
 
@@ -286,7 +301,7 @@ impl Pipeline {
                     resource_threads: state.resource_threads,
                     time_profiler_chan: state.time_profiler_chan,
                     mem_profiler_chan: state.mem_profiler_chan,
-                    window_size: state.window_size,
+                    window_size: window_size,
                     layout_to_constellation_chan: state.layout_to_constellation_chan,
                     script_chan: script_chan.clone(),
                     load_data: state.load_data.clone(),
@@ -301,6 +316,7 @@ impl Pipeline {
                     webvr_chan: state.webvr_chan,
                     webxr_registry: state.webxr_registry,
                     player_context: state.player_context,
+                    device_pixels_per_px: state.device_pixels_per_px,
                 };
 
                 // Spawn the child process.
@@ -507,6 +523,7 @@ pub struct UnprivilegedPipelineContent {
     webvr_chan: Option<IpcSender<WebVRMsg>>,
     webxr_registry: webxr_api::Registry,
     player_context: WindowGLContext,
+    device_pixels_per_px: Option<f32>,
 }
 
 impl UnprivilegedPipelineContent {
@@ -597,7 +614,8 @@ impl UnprivilegedPipelineContent {
             paint_time_metrics,
             layout_thread_busy_flag.clone(),
             self.opts.load_webfonts_synchronously,
-            self.window_size,
+            self.opts.initial_window_size,
+            self.device_pixels_per_px,
             self.opts.dump_display_list,
             self.opts.dump_display_list_json,
             self.opts.dump_style_tree,
diff --git a/components/constellation/session_history.rs b/components/constellation/session_history.rs
index 3e15591215e..0fdcd129baa 100644
--- a/components/constellation/session_history.rs
+++ b/components/constellation/session_history.rs
@@ -3,7 +3,6 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use crate::browsingcontext::NewBrowsingContextInfo;
-use euclid::Size2D;
 use msg::constellation_msg::{
     BrowsingContextId, HistoryStateId, PipelineId, TopLevelBrowsingContextId,
 };
@@ -11,7 +10,6 @@ use script_traits::LoadData;
 use servo_url::ServoUrl;
 use std::cmp::PartialEq;
 use std::{fmt, mem};
-use style_traits::CSSPixel;
 
 /// Represents the joint session history
 /// https://html.spec.whatwg.org/multipage/#joint-session-history
@@ -124,9 +122,6 @@ pub struct SessionHistoryChange {
     /// Holds data for not-yet constructed browsing contexts that are not
     /// easily available when they need to be constructed.
     pub new_browsing_context_info: Option<NewBrowsingContextInfo>,
-
-    /// The size of the viewport for the browsing context.
-    pub window_size: Size2D<f32, CSSPixel>,
 }
 
 /// Represents a pipeline or discarded pipeline in a history entry.
diff --git a/components/layout/display_list/builder.rs b/components/layout/display_list/builder.rs
index c44324d43a1..f951bd3f8f2 100644
--- a/components/layout/display_list/builder.rs
+++ b/components/layout/display_list/builder.rs
@@ -1800,9 +1800,18 @@ impl Fragment {
                         Some(browsing_context_id) => browsing_context_id,
                         None => return warn!("No browsing context id for iframe."),
                     };
+                    let pipeline_id = match fragment_info.pipeline_id {
+                        Some(pipeline_id) => pipeline_id,
+                        None => return warn!("No pipeline id for iframe {}.", browsing_context_id),
+                    };
 
                     let base = create_base_display_item(state);
                     let bounds = stacking_relative_content_box.to_layout();
+                    let item = DisplayItem::Iframe(Box::new(IframeDisplayItem {
+                        base,
+                        bounds,
+                        iframe: pipeline_id,
+                    }));
 
                     // XXXjdm: This sleight-of-hand to convert LayoutRect -> Size2D<CSSPixel>
                     //         looks bogus.
@@ -1811,16 +1820,6 @@ impl Fragment {
                         size: euclid::Size2D::new(bounds.size.width, bounds.size.height),
                     });
 
-                    let pipeline_id = match fragment_info.pipeline_id {
-                        Some(pipeline_id) => pipeline_id,
-                        None => return warn!("No pipeline id for iframe {}.", browsing_context_id),
-                    };
-
-                    let item = DisplayItem::Iframe(Box::new(IframeDisplayItem {
-                        base,
-                        bounds,
-                        iframe: pipeline_id,
-                    }));
                     state.add_display_item(item);
                 }
             },
diff --git a/components/layout/query.rs b/components/layout/query.rs
index 4850b75009c..8dfd1bab795 100644
--- a/components/layout/query.rs
+++ b/components/layout/query.rs
@@ -16,7 +16,6 @@ use crate::sequential;
 use crate::wrapper::LayoutNodeLayoutData;
 use app_units::Au;
 use euclid::default::{Point2D, Rect, Size2D, Vector2D};
-use euclid::Size2D as TypedSize2D;
 use ipc_channel::ipc::IpcSender;
 use msg::constellation_msg::PipelineId;
 use script_layout_interface::rpc::TextIndexResponse;
@@ -41,7 +40,7 @@ use style::dom::TElement;
 use style::logical_geometry::{BlockFlowDirection, InlineBaseDirection, WritingMode};
 use style::properties::{style_structs, LonghandId, PropertyDeclarationId, PropertyId};
 use style::selector_parser::PseudoElement;
-use style_traits::{CSSPixel, ToCss};
+use style_traits::ToCss;
 use webrender_api::ExternalScrollId;
 
 /// Mutable data belonging to the LayoutThread.
@@ -91,9 +90,6 @@ pub struct LayoutThreadData {
 
     /// A queued response for the inner text of a given element.
     pub element_inner_text_response: String,
-
-    /// A queued response for the viewport dimensions for a given browsing context.
-    pub inner_window_dimensions_response: Option<TypedSize2D<f32, CSSPixel>>,
 }
 
 pub struct LayoutRPCImpl(pub Arc<Mutex<LayoutThreadData>>);
@@ -197,12 +193,6 @@ impl LayoutRPC for LayoutRPCImpl {
         let rw_data = rw_data.lock().unwrap();
         rw_data.element_inner_text_response.clone()
     }
-
-    fn inner_window_dimensions(&self) -> Option<TypedSize2D<f32, CSSPixel>> {
-        let &LayoutRPCImpl(ref rw_data) = self;
-        let rw_data = rw_data.lock().unwrap();
-        rw_data.inner_window_dimensions_response.clone()
-    }
 }
 
 struct UnioningFragmentBorderBoxIterator {
diff --git a/components/layout_2020/query.rs b/components/layout_2020/query.rs
index 1317759b33b..23816521c70 100644
--- a/components/layout_2020/query.rs
+++ b/components/layout_2020/query.rs
@@ -7,7 +7,6 @@
 use crate::context::LayoutContext;
 use app_units::Au;
 use euclid::default::{Point2D, Rect};
-use euclid::Size2D;
 use euclid::Vector2D;
 use ipc_channel::ipc::IpcSender;
 use msg::constellation_msg::PipelineId;
@@ -23,7 +22,6 @@ use std::sync::{Arc, Mutex};
 use style::dom::OpaqueNode;
 use style::properties::PropertyId;
 use style::selector_parser::PseudoElement;
-use style_traits::CSSPixel;
 use webrender_api::units::LayoutPixel;
 use webrender_api::ExternalScrollId;
 
@@ -72,9 +70,6 @@ pub struct LayoutThreadData {
 
     /// A queued response for the inner text of a given element.
     pub element_inner_text_response: String,
-
-    /// A queued response for the viewport dimensions for a given browsing context.
-    pub inner_window_dimensions_response: Option<Size2D<f32, CSSPixel>>,
 }
 
 pub struct LayoutRPCImpl(pub Arc<Mutex<LayoutThreadData>>);
@@ -155,12 +150,6 @@ impl LayoutRPC for LayoutRPCImpl {
         let rw_data = rw_data.lock().unwrap();
         rw_data.element_inner_text_response.clone()
     }
-
-    fn inner_window_dimensions(&self) -> Option<Size2D<f32, CSSPixel>> {
-        let &LayoutRPCImpl(ref rw_data) = self;
-        let rw_data = rw_data.lock().unwrap();
-        rw_data.inner_window_dimensions_response.clone()
-    }
 }
 
 pub fn process_content_box_request(_requested_node: OpaqueNode) -> Option<Rect<Au>> {
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 48b7591c242..84ace1c1efe 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -86,13 +86,13 @@ use script_layout_interface::wrapper_traits::LayoutNode;
 use script_traits::Painter;
 use script_traits::{ConstellationControlMsg, LayoutControlMsg, LayoutMsg as ConstellationMsg};
 use script_traits::{DrawAPaintImageResult, IFrameSizeMsg, PaintWorkletError, WindowSizeType};
-use script_traits::{ScrollState, UntrustedNodeAddress, WindowSizeData};
+use script_traits::{ScrollState, UntrustedNodeAddress};
 use selectors::Element;
 use servo_arc::Arc as ServoArc;
 use servo_atoms::Atom;
 use servo_config::opts;
 use servo_config::pref;
-use servo_geometry::MaxRect;
+use servo_geometry::{DeviceIndependentPixel, MaxRect};
 use servo_url::ServoUrl;
 use std::borrow::ToOwned;
 use std::cell::{Cell, RefCell};
@@ -254,6 +254,13 @@ pub struct LayoutThread {
     /// Load web fonts synchronously to avoid non-deterministic network-driven reflows.
     load_webfonts_synchronously: bool,
 
+    /// The initial request size of the window
+    initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+
+    /// The ratio of device pixels per px at the default scale.
+    /// If unspecified, will use the platform default setting.
+    device_pixels_per_px: Option<f32>,
+
     /// Dumps the display list form after a layout.
     dump_display_list: bool,
 
@@ -304,7 +311,8 @@ impl LayoutThreadFactory for LayoutThread {
         paint_time_metrics: PaintTimeMetrics,
         busy: Arc<AtomicBool>,
         load_webfonts_synchronously: bool,
-        window_size: WindowSizeData,
+        initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+        device_pixels_per_px: Option<f32>,
         dump_display_list: bool,
         dump_display_list_json: bool,
         dump_style_tree: bool,
@@ -352,7 +360,8 @@ impl LayoutThreadFactory for LayoutThread {
                         paint_time_metrics,
                         busy,
                         load_webfonts_synchronously,
-                        window_size,
+                        initial_window_size,
+                        device_pixels_per_px,
                         dump_display_list,
                         dump_display_list_json,
                         dump_style_tree,
@@ -522,7 +531,8 @@ impl LayoutThread {
         paint_time_metrics: PaintTimeMetrics,
         busy: Arc<AtomicBool>,
         load_webfonts_synchronously: bool,
-        window_size: WindowSizeData,
+        initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+        device_pixels_per_px: Option<f32>,
         dump_display_list: bool,
         dump_display_list_json: bool,
         dump_style_tree: bool,
@@ -532,10 +542,12 @@ impl LayoutThread {
         trace_layout: bool,
         dump_flow_tree: bool,
     ) -> LayoutThread {
+        // The device pixel ratio is incorrect (it does not have the hidpi value),
+        // but it will be set correctly when the initial reflow takes place.
         let device = Device::new(
             MediaType::screen(),
-            window_size.initial_viewport,
-            window_size.device_pixel_ratio,
+            initial_window_size.to_f32() * Scale::new(1.0),
+            Scale::new(device_pixels_per_px.unwrap_or(1.0)),
         );
 
         // Create the channel on which new animations can be sent.
@@ -597,7 +609,6 @@ impl LayoutThread {
                 text_index_response: TextIndexResponse(None),
                 nodes_from_point_response: vec![],
                 element_inner_text_response: String::new(),
-                inner_window_dimensions_response: None,
             })),
             webrender_image_cache: Arc::new(RwLock::new(FnvHashMap::default())),
             timer: if pref!(layout.animations.test.enabled) {
@@ -610,6 +621,8 @@ impl LayoutThread {
             last_iframe_sizes: Default::default(),
             busy,
             load_webfonts_synchronously,
+            initial_window_size,
+            device_pixels_per_px,
             dump_display_list,
             dump_display_list_json,
             dump_style_tree,
@@ -940,7 +953,8 @@ impl LayoutThread {
             info.paint_time_metrics,
             info.layout_is_busy,
             self.load_webfonts_synchronously,
-            info.window_size,
+            self.initial_window_size,
+            self.device_pixels_per_px,
             self.dump_display_list,
             self.dump_display_list_json,
             self.dump_style_tree,
@@ -1319,9 +1333,6 @@ impl LayoutThread {
                         &QueryMsg::ElementInnerTextQuery(_) => {
                             rw_data.element_inner_text_response = String::new();
                         },
-                        &QueryMsg::InnerWindowDimensionsQuery(_) => {
-                            rw_data.inner_window_dimensions_response = None;
-                        },
                     },
                     ReflowGoal::Full | ReflowGoal::TickAnimations => {},
                 }
@@ -1674,13 +1685,6 @@ impl LayoutThread {
                     rw_data.element_inner_text_response =
                         process_element_inner_text_query(node, &rw_data.indexable_text);
                 },
-                &QueryMsg::InnerWindowDimensionsQuery(browsing_context_id) => {
-                    rw_data.inner_window_dimensions_response = self
-                        .last_iframe_sizes
-                        .borrow()
-                        .get(&browsing_context_id)
-                        .cloned();
-                },
             },
             ReflowGoal::Full | ReflowGoal::TickAnimations => {},
         }
diff --git a/components/layout_thread_2020/lib.rs b/components/layout_thread_2020/lib.rs
index 106dace088b..13cf35975ee 100644
--- a/components/layout_thread_2020/lib.rs
+++ b/components/layout_thread_2020/lib.rs
@@ -67,12 +67,13 @@ use script_layout_interface::rpc::{LayoutRPC, OffsetParentResponse, StyleRespons
 use script_traits::Painter;
 use script_traits::{ConstellationControlMsg, LayoutControlMsg, LayoutMsg as ConstellationMsg};
 use script_traits::{DrawAPaintImageResult, PaintWorkletError};
-use script_traits::{ScrollState, UntrustedNodeAddress, WindowSizeData};
+use script_traits::{ScrollState, UntrustedNodeAddress};
 use selectors::Element;
 use servo_arc::Arc as ServoArc;
 use servo_atoms::Atom;
 use servo_config::opts;
 use servo_config::pref;
+use servo_geometry::DeviceIndependentPixel;
 use servo_url::ServoUrl;
 use std::cell::{Cell, RefCell};
 use std::collections::HashMap;
@@ -211,6 +212,13 @@ pub struct LayoutThread {
     /// Load web fonts synchronously to avoid non-deterministic network-driven reflows.
     load_webfonts_synchronously: bool,
 
+    /// The initial request size of the window
+    initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+
+    /// The ratio of device pixels per px at the default scale.
+    /// If unspecified, will use the platform default setting.
+    device_pixels_per_px: Option<f32>,
+
     /// Emits notifications when there is a relayout.
     relayout_event: bool,
 }
@@ -238,7 +246,8 @@ impl LayoutThreadFactory for LayoutThread {
         paint_time_metrics: PaintTimeMetrics,
         busy: Arc<AtomicBool>,
         load_webfonts_synchronously: bool,
-        window_size: WindowSizeData,
+        initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+        device_pixels_per_px: Option<f32>,
         _dump_display_list: bool,
         _dump_display_list_json: bool,
         _dump_style_tree: bool,
@@ -285,7 +294,8 @@ impl LayoutThreadFactory for LayoutThread {
                         paint_time_metrics,
                         busy,
                         load_webfonts_synchronously,
-                        window_size,
+                        initial_window_size,
+                        device_pixels_per_px,
                         relayout_event,
                     );
 
@@ -447,15 +457,16 @@ impl LayoutThread {
         paint_time_metrics: PaintTimeMetrics,
         busy: Arc<AtomicBool>,
         load_webfonts_synchronously: bool,
-        window_size: WindowSizeData,
+        initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+        device_pixels_per_px: Option<f32>,
         relayout_event: bool,
     ) -> LayoutThread {
         // The device pixel ratio is incorrect (it does not have the hidpi value),
         // but it will be set correctly when the initial reflow takes place.
         let device = Device::new(
             MediaType::screen(),
-            window_size.initial_viewport,
-            window_size.device_pixel_ratio,
+            initial_window_size.to_f32() * Scale::new(1.0),
+            Scale::new(device_pixels_per_px.unwrap_or(1.0)),
         );
 
         // Create the channel on which new animations can be sent.
@@ -512,7 +523,6 @@ impl LayoutThread {
                 text_index_response: TextIndexResponse(None),
                 nodes_from_point_response: vec![],
                 element_inner_text_response: String::new(),
-                inner_window_dimensions_response: None,
             })),
             timer: if pref!(layout.animations.test.enabled) {
                 Timer::test_mode()
@@ -522,6 +532,8 @@ impl LayoutThread {
             paint_time_metrics: paint_time_metrics,
             busy,
             load_webfonts_synchronously,
+            initial_window_size,
+            device_pixels_per_px,
             relayout_event,
         }
     }
@@ -807,7 +819,8 @@ impl LayoutThread {
             info.paint_time_metrics,
             info.layout_is_busy,
             self.load_webfonts_synchronously,
-            info.window_size,
+            self.initial_window_size,
+            self.device_pixels_per_px,
             false, // dump_display_list
             false, // dump_display_list_json
             false, // dump_style_tree
@@ -924,9 +937,6 @@ impl LayoutThread {
                         &QueryMsg::ElementInnerTextQuery(_) => {
                             rw_data.element_inner_text_response = String::new();
                         },
-                        &QueryMsg::InnerWindowDimensionsQuery(_) => {
-                            rw_data.inner_window_dimensions_response = None;
-                        },
                     },
                     ReflowGoal::Full | ReflowGoal::TickAnimations => {},
                 }
@@ -1179,11 +1189,6 @@ impl LayoutThread {
                     let node = unsafe { ServoLayoutNode::new(&node) };
                     rw_data.element_inner_text_response = process_element_inner_text_query(node);
                 },
-                &QueryMsg::InnerWindowDimensionsQuery(_browsing_context_id) => {
-                    // TODO(jdm): port the iframe sizing code from layout2013's display
-                    //            builder in order to support query iframe sizing.
-                    rw_data.inner_window_dimensions_response = None;
-                },
             },
             ReflowGoal::Full | ReflowGoal::TickAnimations => {},
         }
diff --git a/components/layout_traits/lib.rs b/components/layout_traits/lib.rs
index b499bef85c6..cfb824f6c98 100644
--- a/components/layout_traits/lib.rs
+++ b/components/layout_traits/lib.rs
@@ -10,6 +10,7 @@
 //   that these modules won't have to depend on layout.
 
 use crossbeam_channel::{Receiver, Sender};
+use euclid::Size2D;
 use gfx::font_cache_thread::FontCacheThread;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use metrics::PaintTimeMetrics;
@@ -18,7 +19,8 @@ use msg::constellation_msg::{BackgroundHangMonitorRegister, PipelineId};
 use net_traits::image_cache::ImageCache;
 use profile_traits::{mem, time};
 use script_traits::LayoutMsg as ConstellationMsg;
-use script_traits::{ConstellationControlMsg, LayoutControlMsg, WindowSizeData};
+use script_traits::{ConstellationControlMsg, LayoutControlMsg};
+use servo_geometry::DeviceIndependentPixel;
 use servo_url::ServoUrl;
 use std::sync::atomic::AtomicBool;
 use std::sync::Arc;
@@ -46,7 +48,8 @@ pub trait LayoutThreadFactory {
         paint_time_metrics: PaintTimeMetrics,
         busy: Arc<AtomicBool>,
         load_webfonts_synchronously: bool,
-        window_size: WindowSizeData,
+        initial_window_size: Size2D<u32, DeviceIndependentPixel>,
+        device_pixels_per_px: Option<f32>,
         dump_display_list: bool,
         dump_display_list_json: bool,
         dump_style_tree: bool,
diff --git a/components/script/dom/htmliframeelement.rs b/components/script/dom/htmliframeelement.rs
index e58e65ea5bb..f5a820458c2 100644
--- a/components/script/dom/htmliframeelement.rs
+++ b/components/script/dom/htmliframeelement.rs
@@ -28,6 +28,7 @@ use crate::dom::windowproxy::WindowProxy;
 use crate::script_thread::ScriptThread;
 use crate::task_source::TaskSource;
 use dom_struct::dom_struct;
+use euclid::Size2D;
 use html5ever::{LocalName, Prefix};
 use ipc_channel::ipc;
 use msg::constellation_msg::{BrowsingContextId, PipelineId, TopLevelBrowsingContextId};
@@ -172,13 +173,6 @@ impl HTMLIFrameElement {
             replace: replace,
         };
 
-        let window_size = WindowSizeData {
-            initial_viewport: window
-                .inner_window_dimensions_query(browsing_context_id)
-                .unwrap_or_default(),
-            device_pixel_ratio: window.device_pixel_ratio(),
-        };
-
         match nav_type {
             NavigationType::InitialAboutBlank => {
                 let (pipeline_sender, pipeline_receiver) = ipc::channel().unwrap();
@@ -190,7 +184,6 @@ impl HTMLIFrameElement {
                     load_data: load_data.clone(),
                     old_pipeline_id: old_pipeline_id,
                     sandbox: sandboxed,
-                    window_size,
                 };
                 global_scope
                     .script_to_constellation_chan()
@@ -205,7 +198,13 @@ impl HTMLIFrameElement {
                     opener: None,
                     load_data: load_data,
                     pipeline_port: pipeline_receiver,
-                    window_size,
+                    window_size: WindowSizeData {
+                        initial_viewport: {
+                            let rect = self.upcast::<Node>().bounding_content_box_or_zero();
+                            Size2D::new(rect.size.width.to_f32_px(), rect.size.height.to_f32_px())
+                        },
+                        device_pixel_ratio: window.device_pixel_ratio(),
+                    },
                 };
 
                 self.pipeline_id.set(Some(new_pipeline_id));
@@ -217,7 +216,6 @@ impl HTMLIFrameElement {
                     load_data: load_data,
                     old_pipeline_id: old_pipeline_id,
                     sandbox: sandboxed,
-                    window_size,
                 };
                 global_scope
                     .script_to_constellation_chan()
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 95326b46352..70099ee5866 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -89,7 +89,7 @@ use js::jsval::{JSVal, NullValue};
 use js::rust::wrappers::JS_DefineProperty;
 use js::rust::{CustomAutoRooter, CustomAutoRooterGuard, HandleValue};
 use media::WindowGLContext;
-use msg::constellation_msg::{BrowsingContextId, PipelineId};
+use msg::constellation_msg::PipelineId;
 use net_traits::image_cache::{ImageCache, ImageResponder, ImageResponse};
 use net_traits::image_cache::{PendingImageId, PendingImageResponse};
 use net_traits::storage_thread::StorageType;
@@ -1829,16 +1829,6 @@ impl Window {
         DOMString::from(resolved)
     }
 
-    pub fn inner_window_dimensions_query(
-        &self,
-        browsing_context: BrowsingContextId,
-    ) -> Option<Size2D<f32, CSSPixel>> {
-        if !self.layout_reflow(QueryMsg::InnerWindowDimensionsQuery(browsing_context)) {
-            return None;
-        }
-        self.layout_rpc.inner_window_dimensions()
-    }
-
     #[allow(unsafe_code)]
     pub fn offset_parent_query(&self, node: &Node) -> (Option<DomRoot<Element>>, UntypedRect<Au>) {
         if !self.layout_reflow(QueryMsg::OffsetParentQuery(node.to_opaque())) {
@@ -2369,7 +2359,6 @@ fn debug_reflow_events(id: PipelineId, reflow_goal: &ReflowGoal, reason: &Reflow
             &QueryMsg::StyleQuery(_n) => "\tStyleQuery",
             &QueryMsg::TextIndexQuery(..) => "\tTextIndexQuery",
             &QueryMsg::ElementInnerTextQuery(_) => "\tElementInnerTextQuery",
-            &QueryMsg::InnerWindowDimensionsQuery(_) => "\tInnerWindowDimensionsQuery",
         },
     });
 
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 191df335ec5..6a7a69651e7 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -2392,7 +2392,6 @@ impl ScriptThread {
                 load_data.url.clone(),
             ),
             layout_is_busy: layout_is_busy.clone(),
-            window_size,
         });
 
         // Pick a layout thread, any layout thread
@@ -3697,15 +3696,6 @@ impl ScriptThread {
         };
 
         let window = document.window();
-        if window.window_size() == new_size {
-            return;
-        }
-        debug!(
-            "resizing pipeline {:?} from {:?} to {:?}",
-            pipeline_id,
-            window.window_size(),
-            new_size
-        );
         window.set_window_size(new_size);
         window.force_reflow(ReflowGoal::Full, ReflowReason::WindowResize);
 
diff --git a/components/script_layout_interface/Cargo.toml b/components/script_layout_interface/Cargo.toml
index 2e436761dc8..8ad33fc7d43 100644
--- a/components/script_layout_interface/Cargo.toml
+++ b/components/script_layout_interface/Cargo.toml
@@ -33,5 +33,4 @@ servo_arc = {path = "../servo_arc"}
 servo_atoms = {path = "../atoms"}
 servo_url = {path = "../url"}
 style = {path = "../style", features = ["servo"]}
-style_traits = {path = "../style_traits", features = ["servo"]}
 webrender_api = {git = "https://github.com/servo/webrender", features = ["ipc"]}
diff --git a/components/script_layout_interface/message.rs b/components/script_layout_interface/message.rs
index fb2bac65d07..01a589d53cb 100644
--- a/components/script_layout_interface/message.rs
+++ b/components/script_layout_interface/message.rs
@@ -10,7 +10,7 @@ use euclid::default::{Point2D, Rect};
 use gfx_traits::Epoch;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use metrics::PaintTimeMetrics;
-use msg::constellation_msg::{BackgroundHangMonitorRegister, BrowsingContextId, PipelineId};
+use msg::constellation_msg::{BackgroundHangMonitorRegister, PipelineId};
 use net_traits::image_cache::ImageCache;
 use profile_traits::mem::ReportsChan;
 use script_traits::Painter;
@@ -128,7 +128,6 @@ pub enum QueryMsg {
     ResolvedStyleQuery(TrustedNodeAddress, Option<PseudoElement>, PropertyId),
     StyleQuery(TrustedNodeAddress),
     ElementInnerTextQuery(TrustedNodeAddress),
-    InnerWindowDimensionsQuery(BrowsingContextId),
 }
 
 /// Any query to perform with this reflow.
@@ -148,7 +147,6 @@ impl ReflowGoal {
             ReflowGoal::LayoutQuery(ref querymsg, _) => match *querymsg {
                 QueryMsg::NodesFromPointQuery(..) |
                 QueryMsg::TextIndexQuery(..) |
-                QueryMsg::InnerWindowDimensionsQuery(_) |
                 QueryMsg::ElementInnerTextQuery(_) => true,
                 QueryMsg::ContentBoxQuery(_) |
                 QueryMsg::ContentBoxesQuery(_) |
@@ -178,7 +176,6 @@ impl ReflowGoal {
                 QueryMsg::NodeScrollIdQuery(_) |
                 QueryMsg::ResolvedStyleQuery(..) |
                 QueryMsg::OffsetParentQuery(_) |
-                QueryMsg::InnerWindowDimensionsQuery(_) |
                 QueryMsg::StyleQuery(_) => false,
             },
         }
@@ -230,5 +227,4 @@ pub struct LayoutThreadInit {
     pub image_cache: Arc<dyn ImageCache>,
     pub paint_time_metrics: PaintTimeMetrics,
     pub layout_is_busy: Arc<AtomicBool>,
-    pub window_size: WindowSizeData,
 }
diff --git a/components/script_layout_interface/rpc.rs b/components/script_layout_interface/rpc.rs
index 19da8fa6afc..95d25082ed8 100644
--- a/components/script_layout_interface/rpc.rs
+++ b/components/script_layout_interface/rpc.rs
@@ -4,11 +4,9 @@
 
 use app_units::Au;
 use euclid::default::Rect;
-use euclid::Size2D;
 use script_traits::UntrustedNodeAddress;
 use servo_arc::Arc;
 use style::properties::ComputedValues;
-use style_traits::CSSPixel;
 use webrender_api::ExternalScrollId;
 
 /// Synchronous messages that script can send to layout.
@@ -41,8 +39,6 @@ pub trait LayoutRPC {
     fn nodes_from_point_response(&self) -> Vec<UntrustedNodeAddress>;
     /// Query layout to get the inner text for a given element.
     fn element_inner_text(&self) -> String;
-    /// Get the dimensions of an iframe's inner window.
-    fn inner_window_dimensions(&self) -> Option<Size2D<f32, CSSPixel>>;
 }
 
 pub struct ContentBoxResponse(pub Option<Rect<Au>>);
diff --git a/components/script_traits/lib.rs b/components/script_traits/lib.rs
index 468cfb19fb3..9dd0ba04134 100644
--- a/components/script_traits/lib.rs
+++ b/components/script_traits/lib.rs
@@ -739,8 +739,6 @@ pub struct IFrameLoadInfoWithData {
     pub old_pipeline_id: Option<PipelineId>,
     /// Sandbox type of this iframe
     pub sandbox: IFrameSandboxState,
-    /// The initial viewport size for this iframe.
-    pub window_size: WindowSizeData,
 }
 
 /// Specifies whether the script or layout thread needs to be ticked for animation.
@@ -762,7 +760,7 @@ pub struct ScrollState {
 }
 
 /// Data about the window size.
-#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
+#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, Serialize)]
 pub struct WindowSizeData {
     /// The size of the initial layout viewport, before parsing an
     /// <http://www.w3.org/TR/css-device-adapt/#initial-viewport>
diff --git a/components/servo/lib.rs b/components/servo/lib.rs
index 9a39856c762..71430b3f6f4 100644
--- a/components/servo/lib.rs
+++ b/components/servo/lib.rs
@@ -84,7 +84,7 @@ use constellation::{FromCompositorLogger, FromScriptLogger};
 use crossbeam_channel::{unbounded, Sender};
 use embedder_traits::{EmbedderMsg, EmbedderProxy, EmbedderReceiver, EventLoopWaker};
 use env_logger::Builder as EnvLoggerBuilder;
-use euclid::{Scale, Size2D};
+use euclid::Size2D;
 #[cfg(all(
     not(target_os = "windows"),
     not(target_os = "ios"),
@@ -104,9 +104,7 @@ use profile::mem as profile_mem;
 use profile::time as profile_time;
 use profile_traits::mem;
 use profile_traits::time;
-use script_traits::{
-    ConstellationMsg, SWManagerSenders, ScriptToConstellationChan, WindowSizeData,
-};
+use script_traits::{ConstellationMsg, SWManagerSenders, ScriptToConstellationChan};
 use servo_config::opts;
 use servo_config::{pref, prefs};
 use servo_media::player::context::GlContext;
@@ -315,7 +313,11 @@ impl<Window> Servo<Window>
 where
     Window: WindowMethods + 'static + ?Sized,
 {
-    pub fn new(mut embedder: Box<dyn EmbedderMethods>, window: Rc<Window>) -> Servo<Window> {
+    pub fn new(
+        mut embedder: Box<dyn EmbedderMethods>,
+        window: Rc<Window>,
+        device_pixels_per_px: Option<f32>,
+    ) -> Servo<Window> {
         // Global configuration options, parsed from the command line.
         let opts = opts::get();
 
@@ -356,8 +358,6 @@ where
         let devtools_chan = opts.devtools_port.map(|port| devtools::start_server(port));
 
         let coordinates = window.get_coordinates();
-        let device_pixel_ratio = coordinates.hidpi_factor.get();
-        let viewport_size = coordinates.viewport.size.to_f32() / device_pixel_ratio;
 
         let (mut webrender, webrender_api_sender) = {
             let renderer_kind = if opts::get().should_use_osmesa() {
@@ -380,7 +380,12 @@ where
             let render_notifier = Box::new(RenderNotifier::new(compositor_proxy.clone()));
 
             // Cast from `DeviceIndependentPixel` to `DevicePixel`
-            let window_size = Size2D::from_untyped(viewport_size.to_i32().to_untyped());
+            let device_pixel_ratio = coordinates.hidpi_factor.get();
+            let window_size = Size2D::from_untyped(
+                (opts.initial_window_size.to_f32() / device_pixel_ratio)
+                    .to_i32()
+                    .to_untyped(),
+            );
 
             webrender::Renderer::new(
                 window.gl(),
@@ -487,13 +492,6 @@ where
 
         let event_loop_waker = None;
 
-        // The division by 1 represents the page's default zoom of 100%,
-        // and gives us the appropriate CSSPixel type for the viewport.
-        let window_size = WindowSizeData {
-            initial_viewport: viewport_size / Scale::new(1.0),
-            device_pixel_ratio: Scale::new(device_pixel_ratio),
-        };
-
         // Create the constellation, which maintains the engine
         // pipelines, including the script and layout threads, as well
         // as the navigation context.
@@ -515,7 +513,7 @@ where
             webvr_constellation_sender,
             glplayer_threads,
             event_loop_waker,
-            window_size,
+            device_pixels_per_px,
         );
 
         // Send the constellation's swmanager sender to service worker manager thread
@@ -547,6 +545,7 @@ where
             opts.is_running_problem_test,
             opts.exit_after_load,
             opts.convert_mouse_to_touch,
+            device_pixels_per_px,
         );
 
         Servo {
@@ -829,7 +828,7 @@ fn create_constellation(
     webvr_constellation_sender: Option<Sender<Sender<ConstellationMsg>>>,
     glplayer_threads: Option<GLPlayerThreads>,
     event_loop_waker: Option<Box<dyn EventLoopWaker>>,
-    initial_window_size: WindowSizeData,
+    device_pixels_per_px: Option<f32>,
 ) -> (Sender<ConstellationMsg>, SWManagerSenders) {
     // Global configuration options, parsed from the command line.
     let opts = opts::get();
@@ -872,6 +871,7 @@ fn create_constellation(
         glplayer_threads,
         player_context,
         event_loop_waker,
+        device_pixels_per_px,
     };
     let (constellation_chan, from_swmanager_sender) = Constellation::<
         script_layout_interface::message::Msg,
@@ -879,7 +879,8 @@ fn create_constellation(
         script::script_thread::ScriptThread,
     >::start(
         initial_state,
-        initial_window_size,
+        opts.initial_window_size,
+        device_pixels_per_px,
         opts.random_pipeline_closure_probability,
         opts.random_pipeline_closure_seed,
         opts.is_running_problem_test,