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

Source/core/timing/WorkerPerformance.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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 34 matching lines @@
 
 class WorkerPerformance final : public PerformanceBase, public ContextLifecycleObserver {
     DEFINE_WRAPPERTYPEINFO();
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(WorkerPerformance);
 public:
     static WorkerPerformance* create(WorkerGlobalScope* context)
     {
         return new WorkerPerformance(context);
     }
 
-    virtual ExecutionContext* executionContext() const override;
+    ExecutionContext* executionContext() const override;
 
     MemoryInfo* memory();
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit WorkerPerformance(WorkerGlobalScope*);
 };
 
 } // namespace blink
 
 #endif // WorkerPerformance_h