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

tools/gn/target.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_TARGET_H_
 #define TOOLS_GN_TARGET_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 34 matching lines @@
 
   enum DepsIterationType {
     DEPS_ALL,  // Iterates through all public, private, and data deps.
     DEPS_LINKED,  // Iterates through all non-data dependencies.
   };
 
   typedef std::vector<SourceFile> FileList;
   typedef std::vector<std::string> StringVector;
 
   Target(const Settings* settings, const Label& label);
-  virtual ~Target();
+  ~Target() override;
 
   // Returns a string naming the output type.
   static const char* GetStringForOutputType(OutputType type);
 
   // Item overrides.
-  virtual Target* AsTarget() OVERRIDE;
-  virtual const Target* AsTarget() const OVERRIDE;
-  virtual bool OnResolved(Err* err) OVERRIDE;
+  Target* AsTarget() OVERRIDE;
+  const Target* AsTarget() const OVERRIDE;
+  bool OnResolved(Err* err) OVERRIDE;
 
   OutputType output_type() const { return output_type_; }
   void set_output_type(OutputType t) { output_type_ = t; }
 
   // Can be linked into other targets.
   bool IsLinkable() const;
 
   // Can have dependencies linked in.
   bool IsFinal() const;
 
@@ skipping 235 matching lines @@
   const Toolchain* toolchain_;
 
   // Output files. Null until the target is resolved.
   OutputFile link_output_file_;
   OutputFile dependency_output_file_;
 
   DISALLOW_COPY_AND_ASSIGN(Target);
 };
 
 #endif  // TOOLS_GN_TARGET_H_