Fix virtual/override/final usage in Source/core/dom/.

Source/core/dom/TemplateContentDocumentFragment.h

 /*
  * Copyright (C) 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 38 matching lines @@
         DocumentFragment::trace(visitor);
     }
 
 private:
     TemplateContentDocumentFragment(Document& document, Element* host)
         : DocumentFragment(&document, CreateDocumentFragment)
         , m_host(host)
     {
     }
 
-    virtual bool isTemplateContent() const override { return true; }
+    bool isTemplateContent() const override { return true; }
 
     RawPtrWillBeMember<Element> m_host;
 };
 
 } // namespace blink
 
 #endif // TemplateContentDocumentFragment_h