Fix virtual/override/final usage in the rest of Source/core/.

Source/core/events/ClipboardEvent.h

Index: Source/core/events/ClipboardEvent.h
diff --git a/Source/core/events/ClipboardEvent.h b/Source/core/events/ClipboardEvent.h
index 76f7de2ac931df6e1d9257fb871d5d13c3d9fd3c..65829ae2118425579f5edebe07353339d1958c9c 100644
--- a/Source/core/events/ClipboardEvent.h
+++ b/Source/core/events/ClipboardEvent.h
@@ -32,7 +32,7 @@ namespace blink {
 class ClipboardEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    virtual ~ClipboardEvent();
+    ~ClipboardEvent() override;
     static PassRefPtrWillBeRawPtr<ClipboardEvent> create()
     {
         return adoptRefWillBeNoop(new ClipboardEvent());
@@ -51,8 +51,8 @@ private:
     ClipboardEvent();
     ClipboardEvent(const AtomicString& type, bool canBubble, bool cancelable, DataTransfer* clipboardData);
 
-    virtual const AtomicString& interfaceName() const override;
-    virtual bool isClipboardEvent() const override;
+    const AtomicString& interfaceName() const override;
+    bool isClipboardEvent() const override;
 
     PersistentWillBeMember<DataTransfer> m_clipboardData;
 };