Bug 1767253 [wpt PR 33894] - Set fragment index to 0 when hit-testing in non-fragment...

Bug 1767253 [wpt PR 33894] - Set fragment index to 0 when hit-testing in non-fragmented container., a=testonly

Automatic update from web-platform-tests
Set fragment index to 0 when hit-testing in non-fragmented container.

Set the fragment index to 0, instead of leaving it at WTF::kNotFound,
when AppendSingleFragmentForHitTesting() has no container_fragment
specified. container_fragment is nullptr as an optimization, when
the container only has one fragment. See near the end of
HitTestLayerByApplyingTransform().

Bug: 1321302
Change-Id: Ibf6bfce2308229030304d99588defd9494ec0298
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3620315
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1000919}

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wpt-commits: d18cf39d92d0116ae11a6aa034d9fe2f753ce304
wpt-pr: 33894