This has failed once so far:
It's possible that the test is making timing assumptions that don't hold in WebKit, in particular about the timing of event delivery vs the timing of rAF.
The flakiness was fixed by upstream commit https://github.com/w3c/web-platform-tests/commit/03a684d63e62d85cffed38bc942f468692d7d54f, which was downstreamed in https://trac.webkit.org/changeset/227054.
So all that's left to do here is to remove the test expectation line.
Created attachment 331616 [details]
Remove line in TestExpectations
Comment on attachment 331616 [details]
Clearing flags on attachment: 331616
Committed r227139: <https://trac.webkit.org/changeset/227139>
All reviewed patches have been landed. Closing bug.