bug 1082206 detach TrackBuffer when unlinking SourceBuffer r=kinetik

When HTMLMediaElement initiates MediaSourceDecoder Shutdown() in cycle
collection, it may no longer have access to the SourceBuffers to notify
through Detach().

The DiscardDecoder() call in TrackBuffer::Shutdown() is too late as this runs
after MediaDecoderStateMachine::FlushDecoding(), which waits for decode tasks
waiting on the MediaSourceResource.

--HG--
extra : rebase_source : 67e276044a251556eda2186d044c7f6b1f4363cd
extra : histedit_source : 4d921a5d2f4c0bce9ed67a3cb769c0d407662d6c

content/media/mediasource/SourceBuffer.cpp

@@ -416,8 +416,21 @@ SourceBuffer::Dump(const char* aPath)
 }
 #endif
 
-NS_IMPL_CYCLE_COLLECTION_INHERITED(SourceBuffer, DOMEventTargetHelper,
-                                   mMediaSource)
+NS_IMPL_CYCLE_COLLECTION_CLASS(SourceBuffer)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(SourceBuffer)
+  // Tell the TrackBuffer to end its current SourceBufferResource.
+  TrackBuffer* track = tmp->mTrackBuffer;
+  if (track) {
+    track->Detach();
+  }
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mMediaSource)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END_INHERITED(DOMEventTargetHelper)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(SourceBuffer,
+                                                  DOMEventTargetHelper)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mMediaSource)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_ADDREF_INHERITED(SourceBuffer, DOMEventTargetHelper)
 NS_IMPL_RELEASE_INHERITED(SourceBuffer, DOMEventTargetHelper)

content/media/mediasource/TrackBuffer.cpp

@@ -70,10 +70,6 @@ private:
 void
 TrackBuffer::Shutdown()
 {
-  // End the SourceBufferResource associated with mCurrentDecoder, which will
-  // unblock any decoder initialization in ReadMetadata().
-  DiscardDecoder();
-
   // Finish any decoder initialization, which may add to mInitializedDecoders.
   // Shutdown waits for any pending events, which may require the monitor,
   // so we must not hold the monitor during this call.