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

Source/core/dom/DatasetDOMStringMap.h

 /*
  * Copyright (C) 2010 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 24 matching lines @@
 class ExceptionState;
 
 class DatasetDOMStringMap final : public DOMStringMap {
 public:
     static PassOwnPtrWillBeRawPtr<DatasetDOMStringMap> create(Element* element)
     {
         return adoptPtrWillBeNoop(new DatasetDOMStringMap(element));
     }
 
 #if !ENABLE(OILPAN)
-    virtual void ref() override;
-    virtual void deref() override;
+    void ref() override;
+    void deref() override;
 #endif
 
-    virtual void getNames(Vector<String>&) override;
-    virtual String item(const String& name) override;
-    virtual bool contains(const String& name) override;
-    virtual void setItem(const String& name, const String& value, ExceptionState&) override;
-    virtual bool deleteItem(const String& name) override;
+    void getNames(Vector<String>&) override;
+    String item(const String& name) override;
+    bool contains(const String& name) override;
+    void setItem(const String& name, const String& value, ExceptionState&) override;
+    bool deleteItem(const String& name) override;
 
-    virtual Element* element() override { return m_element; }
+    Element* element() override { return m_element; }
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit DatasetDOMStringMap(Element* element)
         : m_element(element)
     {
     }
 
     RawPtrWillBeMember<Element> m_element;
 };
 
 } // namespace blink
 
 #endif // DatasetDOMStringMap_h