Seems unneeded.
Created attachment 47972 [details] proposed fix
Committed revision 54252.
I rolled this change out in r54268 since the method that was removed *is* in fact called, and its removal prevented the display of plug-ins that opted in to accelerated compositing.
Where is it called from? I'd like to add a comment explaining it then.
From inside PluginWidgetMac.mm in WebCore.