Protect AudioScheduledSoureNode::m_startTime and m_endTime.

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 70 matching lines @@
 
     // Detune value (deviating from the frequency) in Cents.
     RefPtr<AudioParamHandler> m_detune;
 
     bool m_firstRender;
 
     // 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;
 
-    // This synchronizes process().
-    mutable Mutex m_processLock;
-
     // 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;
 };
 
 class OscillatorNode final : public AudioScheduledSourceNode {
@@ skipping 12 matching lines @@
     OscillatorNode(AbstractAudioContext&, float sampleRate);
     OscillatorHandler& oscillatorHandler() const;
 
     Member<AudioParam> m_frequency;
     Member<AudioParam> m_detune;
 };
 
 } // namespace blink
 
 #endif // OscillatorNode_h