TextTrackCue creates its display lazily, so it might be NULL when removeDisplayTree or setActive(false) is called. Don't bother creating the display tree if we only want to delete it.
Created attachment 219543 [details] Proposed patch
Comment on attachment 219543 [details] Proposed patch r=me.
Comment on attachment 219543 [details] Proposed patch Clearing flags on attachment: 219543 Committed r160777: <http://trac.webkit.org/changeset/160777>
All reviewed patches have been landed. Closing bug.