As found while diagnosing https://bugs.webkit.org/show_bug.cgi?id=164336, we hit the assertion in WebCore/platform/mac/WebVideoFullscreenHUDWindowController.mm timeToString() when running the tests media/modern-media-controls/pip-support/pip-support-click.html and media/modern-media-controls/pip-support/pip-support-enabled.html in succession. Exiting PiP in the first test before moving on to the next one works around the issue.
Created attachment 299627 [details]
Comment on attachment 299627 [details]
Clearing flags on attachment: 299627
Committed r211130: <http://trac.webkit.org/changeset/211130>
All reviewed patches have been landed. Closing bug.