Currently, when we force a sync of the animations, we blindly copy them to the impl thread. This is a problem if the main thread is waiting for a synchronized start time and the animation has already started on the main thread. In this case, we would copy the running animation over to the impl thread, where it would happily tick, but would never send an 'animation started' notification to the main thread. If the main thread animation requires this notification, we must copy the animation over in a 'waiting' state.
Created attachment 143336 [details] Patch
Comment on attachment 143336 [details] Patch Looks good.
Comment on attachment 143336 [details] Patch Clearing flags on attachment: 143336 Committed r118364: <http://trac.webkit.org/changeset/118364>
All reviewed patches have been landed. Closing bug.