Auto merge of #29745 - mrobinson:compositor-side-scroll-tree, r=mukilan

Add a compositor-side scroll tree

This will allow the compositor to properly chain scrolling requests up
when a node has reached the extent of the scroll area. In addition, it
removes the use of the deprecated WebRender `scroll()` API. This fixes
scrolling on servo.org.

---
<!-- 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 #29402.
  - Fix #27996.
  - Fix #27624.
  - Fix #24028.
  - Fix #23918.
  - Fix #21165.
- [x] There are tests for these changes

1 files changed, 5 insertions, 7 deletions

diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 1e8bd2848be..a6b57778185 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -1064,21 +1064,19 @@ impl LayoutThread {
 
                 debug!("Layout done!");
 
-                // TODO: Avoid the temporary conversion and build webrender sc/dl directly!
-                let (builder, compositor_info, is_contentful) =
-                    display_list.convert_to_webrender(self.id);
-
-                let viewport_size = Size2D::new(
+                let viewport_size = webrender_api::units::LayoutSize::new(
                     self.viewport_size.width.to_f32_px(),
                     self.viewport_size.height.to_f32_px(),
                 );
 
+                // TODO: Avoid the temporary conversion and build webrender sc/dl directly!
+                let (builder, compositor_info, is_contentful) =
+                    display_list.convert_to_webrender(self.id, viewport_size);
+
                 let mut epoch = self.epoch.get();
                 epoch.next();
                 self.epoch.set(epoch);
 
-                let viewport_size = webrender_api::units::LayoutSize::from_untyped(viewport_size);
-
                 // Observe notifications about rendered frames if needed right before
                 // sending the display list to WebRender in order to set time related
                 // Progressive Web Metrics.