Switch to standard integer types in tools/.

tools/gn/substitution_list.cc

 // Copyright 2014 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/substitution_list.h"
 
+#include <stddef.h>
 #include <string.h>
 
 #include "tools/gn/value.h"
 
 SubstitutionList::SubstitutionList() {
 }
 
 SubstitutionList::~SubstitutionList() {
 }
 
@@ skipping 43 matching lines @@
   Err err;
   SubstitutionList result;
   result.Parse(input_strings, nullptr, &err);
   return result;
 }
 
 void SubstitutionList::FillRequiredTypes(SubstitutionBits* bits) const {
   for (const auto& item : list_)
     item.FillRequiredTypes(bits);
 }