Add missing virtual keyword for methods with OVERRIDE

Source/core/html/shadow/MediaControlsChromium.h

 /*
  * Copyright (C) 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 24 matching lines @@
 public:
     // Called from port-specific parent create function to create custom controls.
     static PassRefPtr<MediaControlsChromium> createControls(Document&);
 
     virtual void setMediaController(MediaControllerInterface*) OVERRIDE;
 
     virtual void reset() OVERRIDE;
 
     virtual void playbackStarted() OVERRIDE;
 
-    void changedMute() OVERRIDE;
+    virtual void changedMute() OVERRIDE;
 
     virtual void updateCurrentTimeDisplay() OVERRIDE;
 
-    void createTextTrackDisplay() OVERRIDE;
+    virtual void createTextTrackDisplay() OVERRIDE;
 
     virtual void insertTextTrackContainer(PassRefPtr<MediaControlTextTrackContainerElement>);
 
 protected:
     explicit MediaControlsChromium(Document&);
 
     bool initializeControls(Document&);
 
 private:
     MediaControlTimeRemainingDisplayElement* m_durationDisplay;
     MediaControlPanelEnclosureElement* m_enclosure;
 };
 
 }
 
 #endif