Bug 806729 - Port test_bug536567.html to the new per-tab PB APIs; r=jdm

--HG--
rename : layout/forms/test/test_bug536567.html => layout/forms/test/test_bug536567_perwindowpb.html
Bug 824263 - Shutdown: PeerConnectionMedia disconnect_all() + peer_ctx cleanup. r=jesup,ekr
Bug 824851: Fixed RUN_ON_THREAD to not dispatch on own thread. r=ekr
Bug 825651: Cancel asynchronous callbacks for nICEr upon destruction r=abr