C++11 override style change for athena

ui/keyboard/keyboard_controller_observer.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 UI_KEYBOARD_KEYBOARD_CONTROLLER_OBSERVER_H_
 #define UI_KEYBOARD_KEYBOARD_CONTROLLER_OBSERVER_H_
 
 #include "ui/keyboard/keyboard_export.h"
 
 namespace gfx {
 class Rect;
 }
 
 namespace keyboard {
 
 // Observers to the KeyboardController are notified of significant events that
 // occur with the keyboard, such as the bounds or visiility changing.
 class KEYBOARD_EXPORT KeyboardControllerObserver {
  public:
+  virtual ~KeyboardControllerObserver() {}
+
   // Called when the keyboard bounds or visibility are about to change.
   virtual void OnKeyboardBoundsChanging(const gfx::Rect& new_bounds) = 0;
 };
 
 }  // namespace keyboard
 
 #endif  // UI_KEYBOARD_KEYBOARD_CONTROLLER_OBSERVER_H_