Disallow cross-thread Persistent<> read access.

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

 /*
  * Copyright (C) 2012, 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 78 matching lines @@
   // m_virtualReadIndex is a sample-frame index into our buffer representing the
   // current playback position.  Since it's floating-point, it has sub-sample
   // accuracy.
   double m_virtualReadIndex;
 
   // Stores sample-accurate values calculated according to frequency and detune.
   AudioFloatArray m_phaseIncrements;
   AudioFloatArray m_detuneValues;
 
   // This Persistent doesn't make a reference cycle including the owner
-  // OscillatorNode.
-  Persistent<PeriodicWave> m_periodicWave;
+  // OscillatorNode. It is cross-thread, as it will be accessed by the audio
+  // thread.
+  CrossThreadPersistent<PeriodicWave> m_periodicWave;
 };
 
 class OscillatorNode final : public AudioScheduledSourceNode {
   DEFINE_WRAPPERTYPEINFO();
 
  public:
   static OscillatorNode* create(BaseAudioContext&, ExceptionState&);
   static OscillatorNode* create(BaseAudioContext*,
                                 const OscillatorOptions&,
                                 ExceptionState&);
   DECLARE_VIRTUAL_TRACE();
 
   String type() const;
   void setType(const String&, ExceptionState&);
   AudioParam* frequency();
   AudioParam* detune();
   void setPeriodicWave(PeriodicWave*);
 
  private:
   OscillatorNode(BaseAudioContext&);
   OscillatorHandler& oscillatorHandler() const;
 
   Member<AudioParam> m_frequency;
   Member<AudioParam> m_detune;
 };
 
 }  // namespace blink
 
 #endif  // OscillatorNode_h