Implement suspend() and resume() for OfflineAudioContext

Source/modules/webaudio/OfflineAudioDestinationNode.h

Index: Source/modules/webaudio/OfflineAudioDestinationNode.h
diff --git a/Source/modules/webaudio/OfflineAudioDestinationNode.h b/Source/modules/webaudio/OfflineAudioDestinationNode.h
index ca70d96aa1f5974f2f96f337040ff40479475c2d..4f0e146eb03a020add0bb72b943190c2d605c0e0 100644
--- a/Source/modules/webaudio/OfflineAudioDestinationNode.h
+++ b/Source/modules/webaudio/OfflineAudioDestinationNode.h
@@ -46,16 +46,28 @@ public:
     virtual void initialize() override;
     virtual void uninitialize() override;
 
-    // AudioDestinationHandler
+    // Override the one from AudioContext. Create a rendering thread and
+    // initiate rendering loop or resume rendering if already started and
+    // suspended.
     virtual void startRendering() override;
+
+    // There is no support of the explicit stopping in OfflineAudioContext. This
+    // is just to match the class method signature.
     virtual void stopRendering() override;
 
-    virtual float sampleRate()  const override { return m_renderTarget->sampleRate(); }
+    virtual float sampleRate() const override { return m_renderTarget->sampleRate(); }
+
+    // Return the frame position by quantizing the time (in seconds) and
+    // rounding it down to the nearest render quantum boundary.
+    size_t quantizeTimeToRenderQuantum(double when) const;
 
 private:
     OfflineAudioDestinationHandler(AudioNode&, AudioBuffer* renderTarget);
-    void offlineRender();
-    void offlineRenderInternal();
+
+    // For start/suspend/resume rendering in the destination node.
+    void startOfflineRendering();
+    void runOfflineRendering();
+    void finishOfflineRendering();
 
     // For completion callback on main thread.
     void notifyComplete();
@@ -69,7 +81,9 @@ private:
 
     // Rendering thread.
     OwnPtr<WebThread> m_renderThread;
-    bool m_startedRendering;
+
+    size_t m_framesProcessed;
+    size_t m_framesToProcess;
 };
 
 class OfflineAudioDestinationNode final : public AudioDestinationNode {