Switch to standard integer types in tools/.

tools/gn/standard_out.cc

 // 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.
 
 #include "tools/gn/standard_out.h"
 
+#include <stddef.h>
+
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "build/build_config.h"
 #include "tools/gn/switches.h"
 
@@ skipping 257 matching lines @@
       }
     }
 
     OutputString(line + "\n", dec);
   }
 
   if (is_markdown && in_body)
     OutputString("\n```\n");
 }