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

Source/core/dom/CrossThreadTask.h

 /*
  * Copyright (C) 2009-2010 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 83 matching lines @@
 class CallClosureWithExecutionContextTask final : public CallClosureTaskBase<void(ExecutionContext*)> {
 public:
     // Do not use |create| other than in createCrossThreadTask and
     // createSameThreadTask.
     // See http://crbug.com/390851
     static PassOwnPtr<CallClosureWithExecutionContextTask> create(PassOwnPtr<Function<void(ExecutionContext*)>> closure, bool isSameThread = false)
     {
         return adoptPtr(new CallClosureWithExecutionContextTask(closure, isSameThread));
     }
 
-    virtual void performTask(ExecutionContext* context) override
+    void performTask(ExecutionContext* context) override
     {
         checkThread();
         (*m_closure)(context);
     }
 
 private:
     CallClosureWithExecutionContextTask(PassOwnPtr<Function<void(ExecutionContext*)>> closure, bool isSameThread)
         : CallClosureTaskBase<void(ExecutionContext*)>(closure, isSameThread)
     {
     }
@@ skipping 52 matching lines @@
 template<typename C, typename... P, typename... MP,
     typename RETTYPE = PassOwnPtr<ExecutionContextTask>, size_t PS = sizeof...(P), size_t MPS = sizeof...(MP)>
 typename WTF::EnableIf<PS == MPS + 1, RETTYPE>::Type createCrossThreadTask(void (C::*function)(MP...), const P&... parameters)
 {
     return internal::CallClosureTask::create(threadSafeBind(function, parameters...));
 }
 
 } // namespace blink
 
 #endif // CrossThreadTask_h