tree 748c94c270d865dc81e0e9bc889684f4edbd884b
parent c0538d5500ef425b051f7dcb37772af5025324d0
author Xianzhu Wang <wangxianzhu@chromium.org> 1707505647 -0800
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> 1707507430 -0800

[HitTestTransparency] Experimental status

The feature uses cc::HitTestOpacity::kTransparent for pointer-events:
none. The flag is first marked on paint chunks, then PendingLayer and
cc::Layer, by merging cc::HitTestOpacity from merged painted results.
The merge algorithm (which is already ready for HitTestOpaqueness)
can handle cases such as pointer-events:none with pointer-events:auto
descendants (which will be merged into cc::HitTestOpaqueness::kMixed).
cc::Layer::HitTestable() is now based on this flag for blink.

For test coverage, this CL also includes changes to make existing
tests pass or fix existing bugs with the feature:
- LayerTreeHostImpl::BuildHitTestData() now handles a SurfaceLayer
  with pointer-events:none even if it doesn't draw contents, to make
  CrossSiteSubframe/DragAndDropBrowserTest.CrossTabDrag/* pass.
- Correct hit test transparency for scrolling contents.
- Correct hit test transparency for frames under pointer-events:none
  container (b/323688987).
- Correct hit test transparency for scrollbar layers in boxes with
  pointer-events:none (b/324092420).
- New tests.

ClusterTelemetry job shows that it can reduce main thread scrolling (hit test or repaint) by 36% (kFailedHitTest by 40%,
kNonFastScrollableRegion by 67%) compared to HitTestOpaqueness only.

Bug: 40062957, 323688987, 324092420
Change-Id: I224c8e5f047ec27bf4c8957ae59643457cc9252e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5263065
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1258651}