b=914030 shut down an AudioDestinationNode's graph on destruction, if not already r=ehsan

This means that the graph will be shutdown properly, even if the
AudioDestinationNode is unlinked before AudioContext::Shutdown() is called.

Making MediaStreamGraph::DestroyNonRealtimeInstance() idempotent also makes
AudioContext::Shutdown() idempotent.

--HG--
extra : transplant_source : jZ%86%C5%C2n%17%EF%C2%C0y%ED%14%0E%17_dt%0C%07

content/media/MediaStreamGraph.cpp

@@ -2352,9 +2352,12 @@ void
 MediaStreamGraph::DestroyNonRealtimeInstance(MediaStreamGraph* aGraph)
 {
   NS_ASSERTION(NS_IsMainThread(), "Main thread only");
-  MOZ_ASSERT(aGraph != gGraph, "Should not destroy the global graph here");
+  MOZ_ASSERT(aGraph->IsNonRealtime(), "Should not destroy the global graph here");
 
   MediaStreamGraphImpl* graph = static_cast<MediaStreamGraphImpl*>(aGraph);
+  if (graph->mForceShutDown)
+    return; // already done
+
   if (!graph->mNonRealtimeProcessing) {
     // Start the graph, but don't produce anything
     graph->StartNonRealtimeProcessing(0);
@@ -2421,6 +2424,12 @@ MediaStreamGraph::CreateAudioNodeStream(AudioNodeEngine* aEngine,
   return stream;
 }
 
+bool
+MediaStreamGraph::IsNonRealtime() const
+{
+  return this != gGraph;
+}
+
 void
 MediaStreamGraph::StartNonRealtimeProcessing(uint32_t aTicksToProcess)
 {

content/media/MediaStreamGraph.h

@@ -975,6 +975,7 @@ public:
   // Main thread only
   static MediaStreamGraph* GetInstance();
   static MediaStreamGraph* CreateNonRealtimeInstance();
+  // Idempotent
   static void DestroyNonRealtimeInstance(MediaStreamGraph* aGraph);
 
   // Control API.
@@ -1022,6 +1023,8 @@ public:
    * in main-thread stream state.
    */
   int64_t GetCurrentGraphUpdateIndex() { return mGraphUpdatesSent; }
+
+  bool IsNonRealtime() const;
   /**
    * Start processing non-realtime for a specific number of ticks.
    */

content/media/webaudio/AudioContext.h

@@ -79,7 +79,7 @@ public:
     return GetOwner();
   }
 
-  void Shutdown();
+  void Shutdown(); // idempotent
   void Suspend();
   void Resume();
 

content/media/webaudio/AudioDestinationNode.cpp

@@ -235,6 +235,19 @@ AudioDestinationNode::AudioDestinationNode(AudioContext* aContext,
   mStream = graph->CreateAudioNodeStream(engine, MediaStreamGraph::EXTERNAL_STREAM);
 }
 
+void
+AudioDestinationNode::DestroyMediaStream()
+{
+  if (!mStream)
+    return;
+
+  MediaStreamGraph* graph = mStream->Graph();
+  if (graph->IsNonRealtime()) {
+    MediaStreamGraph::DestroyNonRealtimeInstance(graph);
+  }
+  AudioNode::DestroyMediaStream();
+}
+
 uint32_t
 AudioDestinationNode::MaxChannelCount() const
 {

content/media/webaudio/AudioDestinationNode.h

@@ -25,6 +25,8 @@ public:
                        uint32_t aLength = 0,
                        float aSampleRate = 0.0f);
 
+  virtual void DestroyMediaStream() MOZ_OVERRIDE;
+
   NS_DECL_ISUPPORTS_INHERITED
 
   virtual JSObject* WrapObject(JSContext* aCx,