Implement suspend() and resume() for OfflineAudioContext

Source/modules/webaudio/OfflineAudioDestinationNode.h

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 #ifndef OfflineAudioDestinationNode_h
 #define OfflineAudioDestinationNode_h
 
 #include "modules/webaudio/AudioBuffer.h"
+#include "modules/webaudio/AudioContext.h"
 #include "modules/webaudio/AudioDestinationNode.h"
+#include "modules/webaudio/OfflineAudioContext.h"
 #include "public/platform/WebThread.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
 class AudioBus;
 class AudioContext;
+class OfflineAudioContext;
 
 class OfflineAudioDestinationHandler final : public AudioDestinationHandler {
 public:
     static PassRefPtr<OfflineAudioDestinationHandler> create(AudioNode&, AudioBuffer* renderTarget);
     virtual ~OfflineAudioDestinationHandler();
 
     // AudioHandler
     virtual void dispose() override;
     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 block boundary.
+    size_t quantizeTimeToRenderQuantum(double when) const override;
 
 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();
 
     // This AudioHandler renders into this AudioBuffer.
     // This Persistent doesn't make a reference cycle including the owner
     // OfflineAudioDestinationNode.
     Persistent<AudioBuffer> m_renderTarget;
     // Temporary AudioBus for each render quantum.
     RefPtr<AudioBus> m_renderBus;
 
     // Rendering thread.
     OwnPtr<WebThread> m_renderThread;
-    bool m_startedRendering;
+
+    size_t m_framesProcessed;
+    size_t m_framesToProcess;
 };
 
 class OfflineAudioDestinationNode final : public AudioDestinationNode {
 public:
     static OfflineAudioDestinationNode* create(AudioContext*, AudioBuffer* renderTarget);
 
 private:
     OfflineAudioDestinationNode(AudioContext&, AudioBuffer* renderTarget);
 };
 
 } // namespace blink
 
 #endif // OfflineAudioDestinationNode_h