Bug 1693114 [wpt PR 27648] - [CompositeAfterPaint] Handle main thread scrolling chang...

Bug 1693114 [wpt PR 27648] - [CompositeAfterPaint] Handle main thread scrolling change during scroll animation, a=testonly

Automatic update from web-platform-tests
[CompositeAfterPaint] Handle main thread scrolling change during scroll animation

In pre-CAP the situation is handled when composited scrolling layer
changes in CompositedLayerMapping during compositing assignments update.
Not sure how a mere main thread scrolling status change (e.g. adding
background-attachment:fixed to a composited scrolling scroller) is
handled, but a test for the situation passes.

For CAP, now check change of main thread scrolling status in
PaintPropertyTreeBuilder.

The original test for the situation has not been working since we
removed rounded corner as a blocker of composited scrolling. Fix and
modernize it and add wpt tests.

Bug: 1176543
Change-Id: I00595635a7b1a729ddd05173e3452e40c34e52b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2688140
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#855835}

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wpt-commits: 4c56f3ec2751ff5952b317be7e40844c7b6cf914
wpt-pr: 27648