Bug 1247189 - part4 : ensure we always detach TBM from demuxers. r=jya

Ensure the TBM would always be detached from demuxers, before calling
TBM::detach().

MozReview-Commit-ID: DLWZHB3M3GG

--HG--
extra : rebase_source : 9e455022ba9360fb549222e9ad1238a3ae9d88ad

dom/media/mediasource/SourceBuffer.cpp

@@ -579,11 +579,7 @@ SourceBuffer::HighestEndTime()
 NS_IMPL_CYCLE_COLLECTION_CLASS(SourceBuffer)
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(SourceBuffer)
-  // Tell the TrackBuffer to end its current SourceBufferResource.
-  TrackBuffersManager* manager = tmp->mTrackBuffersManager;
-  if (manager) {
-    manager->Detach();
-  }
+  tmp->Detach();
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mMediaSource)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mBuffered)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END_INHERITED(DOMEventTargetHelper)