Protect AudioScheduledSoureNode::m_startTime and m_endTime.

Source/modules/webaudio/AudioBufferSourceNode.cpp

 /*
  * 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 464 matching lines @@
     if (grainDuration < 0) {
         exceptionState.throwDOMException(
             InvalidStateError,
             ExceptionMessages::indexExceedsMinimumBound(
                 "duration",
                 grainDuration,
                 0.0));
         return;
     }
 
+    // This synchronizes with process(). updateSchedulingInfo will read some of the variables being
+    // set here.
+    MutexLocker processLocker(m_processLock);
+
     m_isDurationGiven = isDurationGiven;
     m_isGrain = true;
     m_grainOffset = grainOffset;
     m_grainDuration = grainDuration;
 
     // The node is started. Add a reference to keep us alive so that audio
     // will eventually get played even if Javascript should drop all references
     // to this node. The reference will get dropped when the source has finished
     // playing.
     context()->notifySourceNodeStartedProcessing(node());
@@ skipping 204 matching lines @@
 }
 
 void AudioBufferSourceNode::start(double when, double grainOffset, double grainDuration, ExceptionState& exceptionState)
 {
     audioBufferSourceHandler().start(when, grainOffset, grainDuration, exceptionState);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)