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

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 29 matching lines @@
 
 namespace {
 
 class DispatchCallbackTask final : public ExecutionContextTask {
 public:
     static PassOwnPtr<DispatchCallbackTask> create(StringCallback* callback, const String& data, const String& taskName)
     {
         return adoptPtr(new DispatchCallbackTask(callback, data, taskName));
     }
 
-    virtual void performTask(ExecutionContext*) override
+    void performTask(ExecutionContext*) override
     {
         m_callback->handleEvent(m_data);
     }
 
-    virtual String taskNameForInstrumentation() const override
+    String taskNameForInstrumentation() const override
     {
         return m_taskName;
     }
 
 private:
     DispatchCallbackTask(StringCallback* callback, const String& data, const String& taskName)
         : m_callback(callback)
         , m_data(data)
         , m_taskName(taskName)
     {
     }
 
     Persistent<StringCallback> m_callback;
     const String m_data;
     const String m_taskName;
 };
 
 } // namespace
 
 void StringCallback::scheduleCallback(StringCallback* callback, ExecutionContext* context, const String& data, const String& instrumentationName)
 {
     context->postTask(FROM_HERE, DispatchCallbackTask::create(callback, data, instrumentationName));
 }
 
 } // namespace blink