Correctly get a plug-in's MIME type when it uses WebPluginMIMETypesFilename
<rdar://problem/9162945>
<https://bugs.webkit.org/show_bug.cgi?id=57204> is a necessary follow-on to this. That bug tracks having the plug-in create the file referenced by WebPluginMIMETypesFilename if it doesn't exist.
Created attachment 87102 [details] Patch
Comment on attachment 87102 [details] Patch r=me
Committed r82087: <http://trac.webkit.org/changeset/82087>