Fix threading races on ConvolverNode::m_reverb in ConvolverNode::tailTime()

Source/modules/webaudio/ConvolverNode.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 140 matching lines @@
 }
 
 AudioBuffer* ConvolverNode::buffer()
 {
     ASSERT(isMainThread());
     return m_buffer.get();
 }
 
 double ConvolverNode::tailTime() const
 {
+    MutexLocker locker(m_processLock);

[Raymond Toy, 2013/09/04 16:18:14]

I don't think we want to lock this way because tailTime is called in the audio
thread.  I think a tryLock is better.  I guess we can return infinity or some
large value if we can't acquire a lock.

     return m_reverb ? m_reverb->impulseResponseLength() / static_cast<double>(sampleRate()) : 0;
 }
 
 double ConvolverNode::latencyTime() const
 {
     return m_reverb ? m_reverb->latencyFrames() / static_cast<double>(sampleRate()) : 0;
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)