LayoutTest media/modern-media-controls/tracks-panel/tracks-panel-hide.html is a flaky timeout https://build.webkit.org/results/Apple%20Sierra%20Debug%20WK1%20(Tests)/r211038%20(2629)/results.html https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=media%2Fmodern-media-controls%2Ftracks-panel%2Ftracks-panel-hide.html
This appears to be limited to macOS debug.
Marked test as flaky in http://trac.webkit.org/projects/webkit/changeset/211059
The timeout is caused by the "transitionend" event not being fired.
This looks like a bug in the TracksPanel class where we register for the "transitionend" event at the same time we apply the "fade-out" class that triggers the transition. But in case the value we're animating from is already 0, we won't have a chance to transition and there will be no event. So we need to register for the event first and delay the transition until the next frame.
Created attachment 299631 [details] Patch
Comment on attachment 299631 [details] Patch Clearing flags on attachment: 299631 Committed r211131: <http://trac.webkit.org/changeset/211131>
All reviewed patches have been landed. Closing bug.