When WebProcess sends animation information to UIProcess, It uses the current time(WTF::currentTime) minus the timeOffset to set the start time animation. But there is a latency between the WebProcess and UIProcess communication and sometimes the animation transition starts late.
Created attachment 117221 [details] Patch Proposed patch.
Comment on attachment 117221 [details] Patch Clearing flags on attachment: 117221 Committed r101595: <http://trac.webkit.org/changeset/101595>
All reviewed patches have been landed. Closing bug.