Make almost all public functions in XKeyboard pure virtual

chrome/browser/chromeos/system_key_event_listener.h

 // Copyright (c) 2011 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 CHROME_BROWSER_CHROMEOS_SYSTEM_KEY_EVENT_LISTENER_H_
 #define CHROME_BROWSER_CHROMEOS_SYSTEM_KEY_EVENT_LISTENER_H_
 #pragma once
 
 #if defined(TOOLKIT_USES_GTK)
 #include <gdk/gdk.h>
@@ skipping 81 matching lines @@
   int32 key_volume_down_;
   int32 key_volume_up_;
   int32 key_f6_;
   int32 key_f7_;
   int32 key_f8_;
   int32 key_f9_;
   int32 key_f10_;
 
   bool stopped_;
 
-  const unsigned int num_lock_mask_;
+  unsigned int num_lock_mask_;
   bool num_lock_is_on_;
   bool caps_lock_is_on_;
   ObserverList<CapsLockObserver> caps_lock_observers_;
 
   // Base X ID for events from the XKB extension.
   int xkb_event_base_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemKeyEventListener);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SYSTEM_KEY_EVENT_LISTENER_H_