Convert OVERRIDE -> override and update virtual/final usage in tools/gn/.

tools/gn/toolchain.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_TOOLCHAIN_H_
 #define TOOLS_GN_TOOLCHAIN_H_
 
-#include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string_piece.h"
 #include "tools/gn/item.h"
 #include "tools/gn/label_ptr.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/source_file_type.h"
 #include "tools/gn/substitution_type.h"
 #include "tools/gn/tool.h"
 #include "tools/gn/value.h"
@@ skipping 35 matching lines @@
   static const char* kToolObjCxx;
   static const char* kToolRc;
   static const char* kToolAsm;
   static const char* kToolAlink;
   static const char* kToolSolink;
   static const char* kToolLink;
   static const char* kToolStamp;
   static const char* kToolCopy;
 
   Toolchain(const Settings* settings, const Label& label);
-  virtual ~Toolchain();
+  ~Toolchain() override;
 
   // Item overrides.
-  virtual Toolchain* AsToolchain() override;
-  virtual const Toolchain* AsToolchain() const override;
+  Toolchain* AsToolchain() override;
+  const Toolchain* AsToolchain() const override;
 
   // Returns TYPE_NONE on failure.
   static ToolType ToolNameToType(const base::StringPiece& str);
   static std::string ToolTypeToName(ToolType type);
 
   // Returns null if the tool hasn't been defined.
   const Tool* GetTool(ToolType type) const;
 
   // Set a tool. When all tools are configured, you should call
   // ToolchainSetupComplete().
@@ skipping 42 matching lines @@
   bool setup_complete_;
 
   // Substitutions used by the tools in this toolchain.
   SubstitutionBits substitution_bits_;
 
   LabelTargetVector deps_;
   Scope::KeyValueMap args_;
 };
 
 #endif  // TOOLS_GN_TOOLCHAIN_H_