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

Source/core/events/MutationEvent.h

Index: Source/core/events/MutationEvent.h
diff --git a/Source/core/events/MutationEvent.h b/Source/core/events/MutationEvent.h
index 62c7b866167a68bb819b0d696eafd92644c54d5f..bcff69609a6a52aec266fbb0ed421b28c36cc8db 100644
--- a/Source/core/events/MutationEvent.h
+++ b/Source/core/events/MutationEvent.h
@@ -32,7 +32,7 @@ namespace blink {
 class MutationEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    virtual ~MutationEvent();
+    ~MutationEvent() override;
 
     enum AttrChangeType {
         MODIFICATION    = 1, // NOLINT
@@ -60,7 +60,7 @@ public:
     String attrName() const { return m_attrName; }
     unsigned short attrChange() const { return m_attrChange; }
 
-    virtual const AtomicString& interfaceName() const override;
+    const AtomicString& interfaceName() const override;
 
     DECLARE_VIRTUAL_TRACE();