Bug 1622437 [wpt PR 22250] - Reland "[ScrollTimeline] Support composited scroll-linke...

Bug 1622437 [wpt PR 22250] - Reland "[ScrollTimeline] Support composited scroll-linked Web Animation", a=testonly

Automatic update from web-platform-tests
Reland "[ScrollTimeline] Support composited scroll-linked Web Animation"

This is a reland of 3254ad50926dbbd809cfa45b611d9081772ce7e8

The patch was reverted due to a test being flaky on debug build. It tests
the behavior that when an animation gets cancelled the other animation
that shares the same ScrollTimeline still work correctly. However, the
test is flaky even when no animation gets cancelled. Suspecting it's
related to how the test is written.

The only change from the original patch is adding the flaky test to
TestExpectation.

TBR=majidvp@chromium.org, bokan@chromium.org

Original change's description:
> [ScrollTimeline] Support composited scroll-linked Web Animation
>
> This patch integrates ScrollTimeline with cc::Animation. Major changes
> include:
> 1. blink::ScrollTimeline is able to create its compositor counterpart
> 2. cc::ScrollTimeline is attached to cc::AnimationHost upon creation
> 3. cc::AnimationHost ticks animations based on their timeline type
> 4. Remove scroll_timeline_ from cc::WorkletAnimation and use the unified
>   animation_timeline_.
> 5. Added virtual/threaded/external/wpt/scroll-animations/.
>
> See [1] for more details.
> [1] https://docs.google.com/document/d/1RpJrYIDYHvtu0ia1vPv_EhBfan428QZ2sgsFhtnXb20/edit?usp=sharing
>
> To sheriffs: if any virtual tests become flaky, please add them to
> TestExpectation instead of reverting the change.
>
> Bug: 1023508
> Change-Id: Ib4aa853bda34ce9b2c0abc943be9f99ac81e799a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2084088
> Commit-Queue: Yi Gu <yigu@chromium.org>
> Reviewed-by: David Bokan <bokan@chromium.org>
> Reviewed-by: Majid Valipour <majidvp@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#749389}

Bug: 1023508
Change-Id: Ic91414c192c519ca4943b58ea57f94f5b076dd0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2103293
Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750336}

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wpt-commits: b250a8dade890029370b216997e41b598f13456f
wpt-pr: 22250