Standardize usage of virtual/override/final in tools/gn/

tools/gn/copy_target_generator.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_COPY_TARGET_GENERATOR_H_
 #define TOOLS_GN_COPY_TARGET_GENERATOR_H_
 
 #include "base/compiler_specific.h"
 #include "tools/gn/target_generator.h"
 
 // Populates a Target with the values from a copy rule.
 class CopyTargetGenerator : public TargetGenerator {
  public:
   CopyTargetGenerator(Target* target,
                       Scope* scope,
                       const FunctionCallNode* function_call,
                       Err* err);
   virtual ~CopyTargetGenerator();
 
  protected:
-  virtual void DoRun() OVERRIDE;
+  void DoRun() OVERRIDE;
 
  private:
   void FillDestDir();
 
   DISALLOW_COPY_AND_ASSIGN(CopyTargetGenerator);
 };
 
 #endif  // TOOLS_GN_COPY_TARGET_GENERATOR_H_