[MSE][Mac] Support abort() in SourceBufferPrivateAVFObjC.
https://bugs.webkit.org/show_bug.cgi?id=135163

Reviewed by Brent Fulgham.

Recreate the parser when asked to abort().

* platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm:
(WebCore::SourceBufferPrivateAVFObjC::abort):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@171478 268f45cc-cd09-0410-ab3c-d52691b4dbfc