Make ui::InputDeviceEventObserver provide a default implementation

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 <vector>
 
 #include "ash/ash_export.h"
@@ skipping 31 matching lines @@
       const std::vector<int64>& outputs) const override;
   bool GetResolutionForDisplayId(int64 display_id,
                                  gfx::Size* size) const override;
 
   // Overriden from ui::DisplayConfigurator::Observer:
   void OnDisplayModeChanged(
       const ui::DisplayConfigurator::DisplayStateList& outputs) override;
 
   // Overriden from ui::InputDeviceEventObserver:
   void OnTouchscreenDeviceConfigurationChanged() override;
-  void OnKeyboardDeviceConfigurationChanged() override;
-  void OnMouseDeviceConfigurationChanged() override;
-  void OnTouchpadDeviceConfigurationChanged() override;
 
   // Overriden from ShellObserver:
   void OnAppTerminating() override;
 
   // 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_