Make ui::InputDeviceEventObserver provide a default implementation

ash/virtual_keyboard_controller.h

 // Copyright 2014 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_VIRTUAL_KEYBOARD_CONTROLLER_H_
 #define ASH_VIRTUAL_KEYBOARD_CONTROLLER_H_
 
 #include "ash/ash_export.h"
 #include "ash/shell_observer.h"
 #include "ash/system/tray/system_tray_notifier.h"
@@ skipping 10 matching lines @@
   ~VirtualKeyboardController() override;
 
   // ShellObserver:
   // TODO(rsadam@): Remove when autovirtual keyboard flag is on by default.
   void OnMaximizeModeStarted() override;
   void OnMaximizeModeEnded() override;
 
   // ui::InputDeviceObserver:
   void OnTouchscreenDeviceConfigurationChanged() override;
   void OnKeyboardDeviceConfigurationChanged() override;
-  void OnMouseDeviceConfigurationChanged() override;
-  void OnTouchpadDeviceConfigurationChanged() override;
 
   // Toggles whether the presense of an external keyboard should be ignored
   // when determining whether or not to show the on-screen keyboard.
   void ToggleIgnoreExternalKeyboard();
 
  private:
   // Updates the list of active input devices.
   void UpdateDevices();
 
   // Updates the keyboard state.
@@ skipping 10 matching lines @@
   bool has_touchscreen_;
   // True if the presense of an external keyboard should be ignored.
   bool ignore_external_keyboard_;
 
   DISALLOW_COPY_AND_ASSIGN(VirtualKeyboardController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_VIRTUAL_KEYBOARD_CONTROLLER_H_