Clear DeferredTaskHandler's audio thread ID upon the thread going away.

third_party/WebKit/Source/modules/webaudio/AbstractAudioContext.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 132 matching lines @@
         m_listener = AudioListener::create(*this);
     }
 }
 
 void AbstractAudioContext::clear()
 {
     m_destinationNode.clear();
     // The audio rendering thread is dead.  Nobody will schedule AudioHandler
     // deletion.  Let's do it ourselves.
     deferredTaskHandler().clearHandlersToBeDeleted();
+    deferredTaskHandler().clearAudioThread();
     m_isCleared = true;
 }
 
 void AbstractAudioContext::uninitialize()
 {
     ASSERT(isMainThread());
 
     if (!isDestinationInitialized())
         return;
 
@@ skipping 818 matching lines @@
 
 SecurityOrigin* AbstractAudioContext::getSecurityOrigin() const
 {
     if (getExecutionContext())
         return getExecutionContext()->getSecurityOrigin();
 
     return nullptr;
 }
 
 } // namespace blink