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

Source/core/events/BeforeUnloadEvent.h

Index: Source/core/events/BeforeUnloadEvent.h
diff --git a/Source/core/events/BeforeUnloadEvent.h b/Source/core/events/BeforeUnloadEvent.h
index 3efeb0f495689c450008af3829a169cc202af452..a4e49f42009c9890c0137cc9041fe1f927fce8ea 100644
--- a/Source/core/events/BeforeUnloadEvent.h
+++ b/Source/core/events/BeforeUnloadEvent.h
@@ -32,19 +32,19 @@ namespace blink {
 class BeforeUnloadEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    virtual ~BeforeUnloadEvent();
+    ~BeforeUnloadEvent() override;
 
     static PassRefPtrWillBeRawPtr<BeforeUnloadEvent> create()
     {
         return adoptRefWillBeNoop(new BeforeUnloadEvent);
     }
 
-    virtual bool isBeforeUnloadEvent() const override;
+    bool isBeforeUnloadEvent() const override;
 
     void setReturnValue(const String& returnValue) { m_returnValue = returnValue; }
     String returnValue() const { return m_returnValue; }
 
-    virtual const AtomicString& interfaceName() const override { return EventNames::BeforeUnloadEvent; }
+    const AtomicString& interfaceName() const override { return EventNames::BeforeUnloadEvent; }
 
     DECLARE_VIRTUAL_TRACE();