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

Source/modules/webaudio/ConvolverNode.cpp

Index: Source/modules/webaudio/ConvolverNode.cpp
diff --git a/Source/modules/webaudio/ConvolverNode.cpp b/Source/modules/webaudio/ConvolverNode.cpp
index 36a473f5f4f58cc6649a429c2af5f1f7903032cf..e873b1df12424a606ab7939e46220b6c6a4f59d7 100644
--- a/Source/modules/webaudio/ConvolverNode.cpp
+++ b/Source/modules/webaudio/ConvolverNode.cpp
@@ -158,6 +158,7 @@ AudioBuffer* ConvolverNode::buffer()
 
 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;
 }