Bug 1642484 [wpt PR 23900] - Remove MainThreadScrollingReasons::kHasClipRelatedProper...

Bug 1642484 [wpt PR 23900] - Remove MainThreadScrollingReasons::kHasClipRelatedProperty, a=testonly

Automatic update from web-platform-tests
Remove MainThreadScrollingReasons::kHasClipRelatedProperty

We no longer need to skip composited scrolling for css clip and
clip-path since (perhaps) BlinkGenPropertyTrees.

In compositor, when we hit test on a layer with special clip/mask,
we'll still fallback to main thread hit testing/scrolling because only
the main thread knows which area is hit testable. This is achieved by
 cc::LayerTreeHostImpl::IsInitialScrollHitTestReliable() returning false.

Bug: 1074395
Change-Id: I91260b063879812ca82928fe783de25c4b6732a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225229
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774232}

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wpt-commits: 4c2484a55b58a72b74c0b6c55ab0238cf11efb4a
wpt-pr: 23900

Differential Revision: https://phabricator.services.mozilla.com/D78793