r158599 added a setting to disable video plugin proxy support in HTMLMediaElement. It also caused the media player to be unconditionally cleared in HTMLMediaElement::clearMediaPlayer, which the old code did not do.
<rdar://problem/15540893>
Created attachment 218346 [details] Proposed patch
Comment on attachment 218346 [details] Proposed patch r=me
Committed r160046 - https://trac.webkit.org/r160046