Remove modules/webaudio/MediaElementAudioSourceNode.h dependency from core.

Source/platform/audio/AudioSourceProviderClient.h

 /*
  * Copyright (C) 2011, 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 12 matching lines @@
  */
 
 #ifndef AudioSourceProviderClient_h
 #define AudioSourceProviderClient_h
 
 namespace WebCore {
 
 class AudioSourceProviderClient {
 public:
     virtual void setFormat(size_t numberOfChannels, float sampleRate) = 0;
+    virtual void lock() { };
+    virtual void unlock() { };
 protected:
     virtual ~AudioSourceProviderClient() { }
 };
 
 } // WebCore
 
 #endif // AudioSourceProviderClient_h