[Cocoa] WebM audio goes out-of-sync or stops playing after a seek
<rdar://73471690>
Created attachment 419176 [details] Patch
Created attachment 419179 [details] Patch
Created attachment 419195 [details] Patch for landing
Committed r272353: <https://trac.webkit.org/changeset/272353> All reviewed patches have been landed. Closing bug and clearing flags on attachment 419195 [details].