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

Source/core/dom/DatasetDOMStringMap.h

Index: Source/core/dom/DatasetDOMStringMap.h
diff --git a/Source/core/dom/DatasetDOMStringMap.h b/Source/core/dom/DatasetDOMStringMap.h
index 55d8735e841180757e2ffbc030f4acdb1d76a319..035b313615cda2e951ef74cd7c60377e8c45dacd 100644
--- a/Source/core/dom/DatasetDOMStringMap.h
+++ b/Source/core/dom/DatasetDOMStringMap.h
@@ -42,17 +42,17 @@ public:
     }
 
 #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();