I left a bogus ASSERT in LoadableTextTrack::trackElementIndex when I committed http://trac.webkit.org/changeset/111581. It is perfectly fine for the node to not be in the DOM, and the method handles the situation.
<rdar://problem/11112196>
Created attachment 133569 [details] Proposed patch
Comment on attachment 133569 [details] Proposed patch Clearing flags on attachment: 133569 Committed r111941: <http://trac.webkit.org/changeset/111941>
All reviewed patches have been landed. Closing bug.