WebAudio: Fix AudioNode leak in a case that AudioNode is not disconnected from the graph explicitly.

Source/modules/webaudio/AudioContext.h

Index: Source/modules/webaudio/AudioContext.h
diff --git a/Source/modules/webaudio/AudioContext.h b/Source/modules/webaudio/AudioContext.h
index 52462a91b678158cadb5e841a9679d590ef182d6..9102268fb8eb529bc3b9781c6cf11a1f01e15f95 100644
--- a/Source/modules/webaudio/AudioContext.h
+++ b/Source/modules/webaudio/AudioContext.h
@@ -79,7 +79,10 @@ class WaveShaperNode;
 // AudioContext is the cornerstone of the web audio API and all AudioNodes are created from it.
 // For thread safety between the audio thread and the main thread, it has a rendering graph locking mechanism.
 
-class AudioContext : public RefCountedGarbageCollectedEventTargetWithInlineData<AudioContext>, public ActiveDOMObject {
+class AudioContext
+    : public RefCountedGarbageCollectedEventTargetWithInlineData<AudioContext>
+    , public ActiveDOMObject
+    , private ThreadState::MarkingTask {
     DEFINE_EVENT_TARGET_REFCOUNTING_WILL_BE_REMOVED(RefCountedGarbageCollected<AudioContext>);
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(AudioContext);
     DEFINE_WRAPPERTYPEINFO();
@@ -103,6 +106,8 @@ public:
 
     bool isInitialized() const { return m_isInitialized; }
     bool isOfflineContext() { return m_isOfflineContext; }
+    AudioContextState contextState() const { return m_contextState; }
+    void setLastZombie(void*);
 
     // Document notification
     virtual void stop() override final;
@@ -290,6 +295,10 @@ private:
     void initialize();
     void uninitialize();
 
+    // ThreadState::MarkingTask functions.
+    void willStartMarking(ThreadState&) override;
+    void didFinishMarking(ThreadState&) override;
+
     // ExecutionContext calls stop twice.
     // We'd like to schedule only one stop action for them.
     bool m_isStopScheduled;
@@ -399,6 +408,10 @@ private:
     bool m_didInitializeContextGraphMutex;
     RecursiveMutex m_contextGraphMutex;
     volatile ThreadIdentifier m_audioThread;
+    // Accessing m_last*Zombie should be protected by
+    // m_didInitializeContextGraphMutex.
+    void* m_lastZombie;
+    void* m_lastRemovableZombie;
 
     // Only accessed in the audio thread.
     // Oilpan: Since items are added to these vectors by the audio thread (not registered to Oilpan),