There seem to be some use cases where the HTMLMediaElement may call "prepareToPlay" more than once. This could happen if asset metadata arrives earlier than expected, or if a web page makes the call multiple times.
Instead of asserting when this happens, just return the existing player item.
Created attachment 224268 [details]
Comment on attachment 224268 [details]
Clearing flags on attachment: 224268
Committed r164177: <http://trac.webkit.org/changeset/164177>
All reviewed patches have been landed. Closing bug.