Protect AudioScheduledSoureNode::m_startTime and m_endTime.

Source/modules/webaudio/AudioScheduledSourceNode.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
@@ skipping 85 matching lines @@
 
     // Called when we have no more sound to play or the stop() time has been reached. No onEnded
     // event is called.
     virtual void finishWithoutOnEnded();
 
     // Like finishWithoutOnEnded(), but an onEnded (if specified) is called.
     virtual void finish();
 
     void notifyEnded();
 
+    // This synchronizes with process() and any other method that needs to be synchronized like
+    // setBuffer for AudioBufferSource.
+    mutable Mutex m_processLock;
+
     // m_startTime is the time to start playing based on the context's timeline (0 or a time less than the context's current time means "now").
     double m_startTime; // in seconds
 
     // m_endTime is the time to stop playing based on the context's timeline (0 or a time less than the context's current time means "now").
     // If it hasn't been set explicitly, then the sound will not stop playing (if looping) or will stop when the end of the AudioBuffer
     // has been reached.
     double m_endTime; // in seconds
 
     bool m_hasEndedListener;
 
@@ skipping 15 matching lines @@
     void setOnended(PassRefPtrWillBeRawPtr<EventListener>);
 
 protected:
     explicit AudioScheduledSourceNode(AbstractAudioContext&);
     AudioScheduledSourceHandler& audioScheduledSourceHandler() const;
 };
 
 } // namespace blink
 
 #endif // AudioScheduledSourceNode_h