Auto merge of #22396 - jdm:no-spam-iframe-size, r=asajeffrey

Reduce unnecessary iframe size messages

This should be an improvement on pages that include iframes, since we currently run two layout jobs for every display-oriented layout request. When building the display list, we send a message to the constellation that includes the sizes of all iframes present, and the constellation sends resize messages to the script thread. This results in a mouse event on the outer page causing all frames to be re-laid out even if no changes occurred to the iframe sizes, which is ridiculous.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #22394
- [x] These changes do not require tests because there is no way to test this internal detail.

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components/layout/display_list/builder.rs

@@ -37,9 +37,10 @@ use gfx::text::glyph::ByteIndex;
 use gfx::text::TextRun;
 use gfx_traits::{combine_id_with_fragment_type, FragmentType, StackingContextId};
 use ipc_channel::ipc;
-use msg::constellation_msg::{BrowsingContextId, PipelineId};
+use msg::constellation_msg::PipelineId;
 use net_traits::image_cache::UsePlaceholder;
 use range::Range;
+use script_traits::IFrameSize;
 use servo_config::opts;
 use servo_geometry::MaxRect;
 use std::default::Default;
@@ -61,7 +62,6 @@ use style::values::generics::background::BackgroundSize;
 use style::values::generics::image::{GradientKind, Image, PaintWorklet};
 use style::values::{Either, RGBA};
 use style_traits::cursor::CursorKind;
-use style_traits::CSSPixel;
 use style_traits::ToCss;
 use webrender_api::{
     self, BorderDetails, BorderRadius, BorderSide, BoxShadowClipMode, ColorF, ColorU,
@@ -318,7 +318,7 @@ pub struct DisplayListBuildState<'a> {
 
     /// Vector containing iframe sizes, used to inform the constellation about
     /// new iframe sizes
-    pub iframe_sizes: Vec<(BrowsingContextId, TypedSize2D<f32, CSSPixel>)>,
+    pub iframe_sizes: Vec<IFrameSize>,
 
     /// Stores text runs to answer text queries used to place a cursor inside text.
     pub indexable_text: IndexableText,
@@ -1785,9 +1785,10 @@ impl Fragment {
                     }));
 
                     let size = Size2D::new(item.bounds().size.width, item.bounds().size.height);
-                    state
-                        .iframe_sizes
-                        .push((browsing_context_id, TypedSize2D::from_untyped(&size)));
+                    state.iframe_sizes.push(IFrameSize {
+                        id: browsing_context_id,
+                        size: TypedSize2D::from_untyped(&size),
+                    });
 
                     state.add_display_item(item);
                 }