Disallow cross-thread Persistent<> read access.

third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.h

 /*
  * Copyright (C) 2011, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 88 matching lines @@
 
   // The offline version of render() method. If the rendering needs to be
   // suspended after checking, this stops the rendering and returns true.
   // Otherwise, it returns false after rendering one quantum.
   bool renderIfNotSuspended(AudioBus* sourceBus,
                             AudioBus* destinationBus,
                             size_t numberOfFrames);
 
   // This AudioHandler renders into this AudioBuffer.
   // This Persistent doesn't make a reference cycle including the owner
-  // OfflineAudioDestinationNode.
-  Persistent<AudioBuffer> m_renderTarget;
+  // OfflineAudioDestinationNode. It is accessed by both audio and main thread.
+  CrossThreadPersistent<AudioBuffer> m_renderTarget;
   // Temporary AudioBus for each render quantum.
   RefPtr<AudioBus> m_renderBus;
 
   // Rendering thread.
   std::unique_ptr<WebThread> m_renderThread;
 
   // These variables are for counting the number of frames for the current
   // progress and the remaining frames to be processed.
   size_t m_framesProcessed;
   size_t m_framesToProcess;
@@ skipping 12 matching lines @@
   static OfflineAudioDestinationNode* create(BaseAudioContext*,
                                              AudioBuffer* renderTarget);
 
  private:
   OfflineAudioDestinationNode(BaseAudioContext&, AudioBuffer* renderTarget);
 };
 
 }  // namespace blink
 
 #endif  // OfflineAudioDestinationNode_h