Bug 1306813 - Don't puslish events to mOnOutput after DecodedStream::Stop() is called. r=pehrsons

Because the TaskQueue of MDSM will shut down soon and TaskQueue::Dispatch() will fail (via mOnOutput.Notify()).
We reset mStream in Forget() on the TaskQueue thread of MDSM so NotifyOutput() can check it
and ensure mOnOutput.Notify() always happen before DecodedStream::Stop().

MozReview-Commit-ID: 4sCXk1KAfCC

--HG--
extra : rebase_source : 1ec50a86fa1519c4fc8caa1087f2794411aa23b0

dom/media/mediasink/DecodedStream.cpp

@@ -61,13 +61,16 @@ public:
 
   void DoNotifyFinished()
   {
+    MOZ_ASSERT(NS_IsMainThread());
     mFinishPromise.ResolveIfExists(true, __func__);
   }
 
   void Forget()
   {
-    MOZ_ASSERT(NS_IsMainThread());
-    mFinishPromise.ResolveIfExists(true, __func__);
+    AbstractThread::MainThread()->Dispatch(NS_NewRunnableFunction([this] () {
+      MOZ_ASSERT(NS_IsMainThread());
+      mFinishPromise.ResolveIfExists(true, __func__);
+    }));
     MutexAutoLock lock(mMutex);
     mStream = nullptr;
   }
@@ -123,6 +126,7 @@ public:
   ~DecodedStreamData();
   void SetPlaying(bool aPlaying);
   MediaEventSource<int64_t>& OnOutput();
+  void Forget();
 
   /* The following group of fields are protected by the decoder's monitor
    * and can be read or written on any thread.
@@ -188,7 +192,6 @@ DecodedStreamData::DecodedStreamData(OutputStreamManager* aOutputStreamManager,
 DecodedStreamData::~DecodedStreamData()
 {
   mOutputStreamManager->Disconnect();
-  mListener->Forget();
   mStream->Destroy();
 }
 
@@ -207,6 +210,12 @@ DecodedStreamData::SetPlaying(bool aPlaying)
   }
 }
 
+void
+DecodedStreamData::Forget()
+{
+  mListener->Forget();
+}
+
 DecodedStream::DecodedStream(AbstractThread* aOwnerThread,
                              MediaQueue<MediaData>& aAudioQueue,
                              MediaQueue<MediaData>& aVideoQueue,
@@ -363,6 +372,7 @@ DecodedStream::DestroyData(UniquePtr<DecodedStreamData> aData)
   mOutputListener.Disconnect();
 
   DecodedStreamData* data = aData.release();
+  data->Forget();
   nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction([=] () {
     delete data;
   });