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

Source/core/dom/ExecutionContextTask.h

 /*
  * Copyright (C) 2013 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 72 matching lines @@
 class CallClosureTask final : public CallClosureTaskBase<void()> {
 public:
     // Do not use |create| other than in createCrossThreadTask and
     // createSameThreadTask.
     // See http://crbug.com/390851
     static PassOwnPtr<CallClosureTask> create(PassOwnPtr<Closure> closure, bool isSameThread = false)
     {
         return adoptPtr(new CallClosureTask(closure, isSameThread));
     }
 
-    virtual void performTask(ExecutionContext*) override
+    void performTask(ExecutionContext*) override
     {
         checkThread();
         (*m_closure)();
     }
 
 private:
     CallClosureTask(PassOwnPtr<Closure> closure, bool isSameThread)
         : CallClosureTaskBase<void()>(closure, isSameThread)
     {
     }
 };
 
 } // namespace internal
 
 // Create tasks passed within a single thread.
 // When posting tasks within a thread, use |createSameThreadTask| instead
 // of using |bind| directly to state explicitly that there is no need to care
 // about thread safety when posting the task.
 // When posting tasks across threads, use |createCrossThreadTask|.
 template<typename FunctionType, typename... P>
 PassOwnPtr<ExecutionContextTask> createSameThreadTask(
     FunctionType function, const P&... parameters)
 {
     return internal::CallClosureTask::create(bind(function, parameters...), true);
 }
 
 } // namespace
 
 #endif