Make ui::InputDeviceEventObserver provide a default implementation

ash/virtual_keyboard_controller.cc

 // 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.
 
 #include "ash/virtual_keyboard_controller.h"
 
 #include <vector>
 
 #include "ash/shell.h"
 #include "ash/wm/maximize_mode/maximize_mode_controller.h"
@@ skipping 49 matching lines @@
 }
 
 void VirtualKeyboardController::OnTouchscreenDeviceConfigurationChanged() {
   UpdateDevices();
 }
 
 void VirtualKeyboardController::OnKeyboardDeviceConfigurationChanged() {
   UpdateDevices();
 }
 
-void VirtualKeyboardController::OnMouseDeviceConfigurationChanged() {
-}
-
-void VirtualKeyboardController::OnTouchpadDeviceConfigurationChanged() {
-}
-
 void VirtualKeyboardController::ToggleIgnoreExternalKeyboard() {
   ignore_external_keyboard_ = !ignore_external_keyboard_;
   UpdateKeyboardEnabled();
 }
 
 void VirtualKeyboardController::UpdateDevices() {
   ui::DeviceDataManager* device_data_manager =
       ui::DeviceDataManager::GetInstance();
 
   // Checks for touchscreens.
@@ skipping 36 matching lines @@
   keyboard::SetTouchKeyboardEnabled(enabled);
   if (enabled) {
     Shell::GetInstance()->CreateKeyboard();
   } else {
     if (!keyboard::IsKeyboardEnabled())
       Shell::GetInstance()->DeactivateKeyboard();
   }
 }
 
 }  // namespace ash