Clean forward declaration in public

public/platform/WebAudioBus.h

 /*
  * 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 16 matching lines @@
 
 #include "WebCommon.h"
 
 #if INSIDE_BLINK
 namespace WTF { template <typename T> class PassRefPtr; }
 #endif
 
 namespace blink {
 
 class AudioBus;
-class WebAudioBusPrivate;
 
 // A container for multi-channel linear PCM audio data.
 //
 // WARNING: It is not safe to pass a WebAudioBus across threads!!!
 //
 class BLINK_PLATFORM_EXPORT WebAudioBus {
 public:
     WebAudioBus() : m_private(0) { }
     ~WebAudioBus() { reset(); }
 
@@ skipping 21 matching lines @@
     // Disallow copy and assign.
     WebAudioBus(const WebAudioBus&);
     void operator=(const WebAudioBus&);
 
     AudioBus* m_private;
 };
 
 } // namespace blink
 
 #endif // WebAudioBus_h