Implement suspend() and resume() for OfflineAudioContext

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 9ea7dd20da78526b65d5dd0672f0bbab69918f50..c77474660cde191c8eba85b1e0b6de45d744c966 100644
--- a/Source/modules/webaudio/AudioContext.h
+++ b/Source/modules/webaudio/AudioContext.h
@@ -220,9 +220,13 @@ public:
     DEFINE_ATTRIBUTE_EVENT_LISTENER(statechange);
 
     void startRendering();
-    void fireCompletionEvent();
     void notifyStateChange();
 
+    // From offline rendering.
+    void fireSuspendEvent();
+    void fireCompletionEvent();
+    virtual bool suspendIfNecessary();
+
     // A context is considered closed if:
     //  - closeContext() has been called, even if the audio HW has not yet been
     //    stopped.  It will be stopped eventually.
@@ -240,6 +244,14 @@ protected:
     AudioContext(Document*, unsigned numberOfChannels, size_t numberOfFrames, float sampleRate);
 
     RefPtrWillBeMember<ScriptPromiseResolver> m_offlineResolver;
+    Member<AudioDestinationNode> m_destinationNode;
+    bool m_didInitializeContextGraphMutex;
+    Member<AudioBuffer> m_renderTarget;
+
+    // The state of the AudioContext.
+    void setContextState(AudioContextState);
+    AudioContextState m_contextState;
+
 private:
     void initialize();
     void uninitialize();
@@ -259,7 +271,7 @@ private:
     // haven't finished playing.  Make sure to release them here.
     void releaseActiveSourceNodes();
 
-    Member<AudioDestinationNode> m_destinationNode;
+
     Member<AudioListener> m_listener;
 
     // Only accessed in the audio thread.
@@ -294,18 +306,10 @@ private:
 
     unsigned m_connectionCount;
 
-    // Graph locking.
-    bool m_didInitializeContextGraphMutex;
     RefPtr<DeferredTaskHandler> m_deferredTaskHandler;
 
-    Member<AudioBuffer> m_renderTarget;
-
     bool m_isOfflineContext;
 
-    // The state of the AudioContext.
-    AudioContextState m_contextState;
-    void setContextState(AudioContextState);
-
     AsyncAudioDecoder m_audioDecoder;
 
     // The Promise that is returned by close();