Protect AudioScheduledSoureNode::m_startTime and m_endTime.

Source/modules/webaudio/AudioScheduledSourceNode.cpp

 /*
  * 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 135 matching lines @@
     if (when < 0) {
         exceptionState.throwDOMException(
             InvalidAccessError,
             ExceptionMessages::indexExceedsMinimumBound(
                 "start time",
                 when,
                 0.0));
         return;
     }
 
+    // This synchronizes with process(). updateSchedulingInfo will read some of the variables being
+    // set here.
+    MutexLocker processLocker(m_processLock);
+
     // 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());
 
     // If |when| < currentTime, the source must start now according to the spec.
     // So just set startTime to currentTime in this case to start the source now.
     m_startTime = std::max(when, context()->currentTime());
 
     setPlaybackState(SCHEDULED_STATE);
@@ skipping 13 matching lines @@
     if (when < 0) {
         exceptionState.throwDOMException(
             InvalidAccessError,
             ExceptionMessages::indexExceedsMinimumBound(
                 "stop time",
                 when,
                 0.0));
         return;
     }
 
+    // This synchronizes with process()
+    MutexLocker processLocker(m_processLock);
+
     // stop() can be called more than once, with the last call to stop taking effect, unless the
     // source has already stopped due to earlier calls to stop. No exceptions are thrown in any
     // case.
     when = std::max(0.0, when);
     m_endTime = when;
 }
 
 void AudioScheduledSourceHandler::finishWithoutOnEnded()
 {
     if (playbackState() != FINISHED_STATE) {
@@ skipping 57 matching lines @@
 
 void AudioScheduledSourceNode::setOnended(PassRefPtrWillBeRawPtr<EventListener> listener)
 {
     audioScheduledSourceHandler().setHasEndedListener();
     setAttributeEventListener(EventTypeNames::ended, listener);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)