Protect AudioScheduledSoureNode::m_startTime and m_endTime.

Source/modules/webaudio/AudioBufferSourceNode.h

 /*
  * Copyright (C) 2010, 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 127 matching lines @@
     // We optionally keep track of a panner node which has a doppler shift that
     // is incorporated into the pitch rate.
     // This RefPtr is connection reference. We must call AudioHandler::
     // makeConnection() after ref(), and call AudioHandler::breakConnection()
     // before deref().
     // TODO(tkent): This is always null because setPannerNode is never
     // called. If we revive setPannerNode, this should be a raw pointer and
     // AudioBufferSourceNode should have Member<PannerNode>.
     RefPtr<PannerHandler> m_pannerNode;
 
-    // This synchronizes process() with setBuffer() which can cause dynamic channel count changes.
-    mutable Mutex m_processLock;
-
     // The minimum playbackRate value ever used for this source.  This includes any adjustments
     // caused by doppler too.
     double m_minPlaybackRate;
 };
 
 class AudioBufferSourceNode final : public AudioScheduledSourceNode {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static AudioBufferSourceNode* create(AbstractAudioContext&, float sampleRate);
     DECLARE_VIRTUAL_TRACE();
@@ skipping 18 matching lines @@
 private:
     AudioBufferSourceNode(AbstractAudioContext&, float sampleRate);
 
     Member<AudioParam> m_playbackRate;
     Member<AudioParam> m_detune;
 };
 
 } // namespace blink
 
 #endif // AudioBufferSourceNode_h