Add OVERRIDE where possible in HTMLMediaElement and children

Source/core/html/HTMLAudioElement.h

 /*
  * Copyright (C) 2007, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 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 23 matching lines @@
 class Document;
 
 class HTMLAudioElement FINAL : public HTMLMediaElement {
 public:
     static PassRefPtr<HTMLAudioElement> create(const QualifiedName&, Document&, bool);
     static PassRefPtr<HTMLAudioElement> createForJSConstructor(Document&, const String& src);
 
 private:
     HTMLAudioElement(const QualifiedName&, Document&, bool);
 
-    virtual bool isVideo() const { return false; }
+    virtual bool isVideo() const OVERRIDE { return false; }
 };
 
 } //namespace
 
 #endif