chromeos: Cleanup class/struct fwd declarations

chromeos/audio/audio_devices_pref_handler.h

 // Copyright (c) 2013 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 CHROMEOS_AUDIO_AUDIO_DEVICES_PREF_HANDLER_H_
 #define CHROMEOS_AUDIO_AUDIO_DEVICES_PREF_HANDLER_H_
 
 #include "base/memory/ref_counted.h"
 #include "chromeos/audio/audio_pref_observer.h"
 #include "chromeos/chromeos_export.h"
 
-class PrefService;
-
 namespace chromeos {
 
 struct AudioDevice;
 
 // Interface that handles audio preference related work, reads and writes
 // audio preferences, and notifies AudioPrefObserver for audio preference
 // changes.
 class CHROMEOS_EXPORT AudioDevicesPrefHandler
     : public base::RefCountedThreadSafe<AudioDevicesPrefHandler> {
  public:
@@ skipping 39 matching lines @@
  protected:
   virtual ~AudioDevicesPrefHandler() {}
 
  private:
   friend class base::RefCountedThreadSafe<AudioDevicesPrefHandler>;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_AUDIO_AUDIO_DEVICES_PREF_HANDLER_H_