ash: Cleanup class/struct forward declarations

ash/display/display_change_observer_chromeos.h

 // Copyright 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 ASH_DISPLAY_DISPLAY_CHANGE_OBSERVER_CHROMEOS_H_
 #define ASH_DISPLAY_DISPLAY_CHANGE_OBSERVER_CHROMEOS_H_
 
 #include <stdint.h>
 
 #include <vector>
 
 #include "ash/ash_export.h"
 #include "ash/common/shell_observer.h"
 #include "base/macros.h"
 #include "ui/display/chromeos/display_configurator.h"
 #include "ui/display/manager/managed_display_info.h"
 #include "ui/events/devices/input_device_event_observer.h"
 
 namespace ash {
 
-class DisplayMode;
 class DisplaySnapshot;
 
 // An object that observes changes in display configuration and
 // update DisplayManagers.
 class DisplayChangeObserver : public ui::DisplayConfigurator::StateController,
                               public ui::DisplayConfigurator::Observer,
                               public ui::InputDeviceEventObserver,
                               public ShellObserver {
  public:
   // Returns the mode list for internal display.
@@ skipping 31 matching lines @@
   // Exposed for testing.
   ASH_EXPORT static float FindDeviceScaleFactor(float dpi);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DisplayChangeObserver);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DISPLAY_DISPLAY_CHANGE_OBSERVER_CHROMEOS_H_