content: Cleanup class/struct forward declarations

content/renderer/media/renderer_webaudiodevice_impl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_MEDIA_RENDERER_WEBAUDIODEVICE_IMPL_H_
 #define CONTENT_RENDERER_MEDIA_RENDERER_WEBAUDIODEVICE_IMPL_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread_checker.h"
 #include "media/base/audio_parameters.h"
 #include "media/base/audio_renderer_sink.h"
 #include "third_party/WebKit/public/platform/WebAudioDevice.h"
 #include "third_party/WebKit/public/platform/WebVector.h"
 #include "url/origin.h"
 
-namespace base {
-class SingleThreadTaskRunner;
-}
-
 namespace media {
 class SilentSinkSuspender;
 }
 
 namespace content {
 class RendererWebAudioDeviceImpl
     : public blink::WebAudioDevice,
       public media::AudioRendererSink::RenderCallback {
  public:
   RendererWebAudioDeviceImpl(const media::AudioParameters& params,
@@ skipping 35 matching lines @@
 
   // Used to suspend |sink_| usage when silence has been detected for too long.
   std::unique_ptr<media::SilentSinkSuspender> webaudio_suspender_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererWebAudioDeviceImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_RENDERER_WEBAUDIODEVICE_IMPL_H_