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

Source/core/html/MediaKeyEvent.h

Index: Source/core/html/MediaKeyEvent.h
diff --git a/Source/core/html/MediaKeyEvent.h b/Source/core/html/MediaKeyEvent.h
index ca9d6e643dcd14fbb7ea6e69a21dcd61e923f32a..e2669457071af17cee78742d402e63ee3ec304c9 100644
--- a/Source/core/html/MediaKeyEvent.h
+++ b/Source/core/html/MediaKeyEvent.h
@@ -37,7 +37,7 @@ namespace blink {
 class CORE_EXPORT MediaKeyEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    virtual ~MediaKeyEvent();
+    ~MediaKeyEvent() override;
 
     static PassRefPtrWillBeRawPtr<MediaKeyEvent> create()
     {
@@ -49,7 +49,7 @@ public:
         return adoptRefWillBeNoop(new MediaKeyEvent(type, initializer));
     }
 
-    virtual const AtomicString& interfaceName() const override;
+    const AtomicString& interfaceName() const override;
 
     String keySystem() const { return m_keySystem; }
     String sessionId() const { return m_sessionId; }