bug 1081766 don't clear mDecoders in TrackBuffer::Shutdown so that BreakCycles can recurse r=kinetik

--HG--
extra : rebase_source : a6f20e639b6e71a26fe65ad9cedb8d852f8b31e4
extra : histedit_source : 08a606b2583a442b84d153ad776cc7a87229266b

content/media/mediasource/TrackBuffer.cpp

@@ -91,8 +91,6 @@ TrackBuffer::Shutdown()
     mDecoders[i]->GetReader()->Shutdown();
   }
   mInitializedDecoders.Clear();
-  NS_DispatchToMainThread(new ReleaseDecoderTask(mDecoders));
-  MOZ_ASSERT(mDecoders.IsEmpty());
   mParentDecoder = nullptr;
 }