Update more core classes to use OVERRIDE / FINAL when needed

Source/core/dom/StringCallback.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 21 matching lines @@
 #include "core/dom/StringCallback.h"
 
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/ExecutionContextTask.h"
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
 namespace {
 
-class DispatchCallbackTask : public ExecutionContextTask {
+class DispatchCallbackTask FINAL : public ExecutionContextTask {
 public:
     static PassOwnPtr<DispatchCallbackTask> create(PassOwnPtr<StringCallback> callback, const String& data)
     {
         return adoptPtr(new DispatchCallbackTask(callback, data));
     }
 
-    virtual void performTask(ExecutionContext*)
+    virtual void performTask(ExecutionContext*) OVERRIDE
     {
         m_callback->handleEvent(m_data);
     }
 
 private:
     DispatchCallbackTask(PassOwnPtr<StringCallback> callback, const String& data)
         : m_callback(callback)
         , m_data(data)
     {
     }
 
     OwnPtr<StringCallback> m_callback;
     const String m_data;
 };
 
 } // namespace
 
 void StringCallback::scheduleCallback(PassOwnPtr<StringCallback> callback, ExecutionContext* context, const String& data)
 {
     context->postTask(DispatchCallbackTask::create(callback, data));
 }
 
 } // namespace WebCore