Add support for customizing GN's args text.

tools/gn/build_settings.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/build_settings.h"
 
 #include <utility>
 
 #include "base/files/file_util.h"
 #include "tools/gn/filesystem_utils.h"
 
 BuildSettings::BuildSettings() {
 }
 
 BuildSettings::BuildSettings(const BuildSettings& other)
     : root_path_(other.root_path_),
       root_path_utf8_(other.root_path_utf8_),
       secondary_source_path_(other.secondary_source_path_),
       python_path_(other.python_path_),
       build_config_file_(other.build_config_file_),
+      arg_file_template_path_(other.arg_file_template_path_),
       build_dir_(other.build_dir_),
       build_args_(other.build_args_) {
 }
 
 BuildSettings::~BuildSettings() {
 }
 
 void BuildSettings::SetRootPath(const base::FilePath& r) {
   DCHECK(r.value()[r.value().size() - 1] != base::FilePath::kSeparators[0]);
   root_path_ = r.NormalizePathSeparatorsTo('/');
@@ skipping 24 matching lines @@
 base::FilePath BuildSettings::GetFullPathSecondary(
     const SourceDir& dir) const {
   return dir.Resolve(secondary_source_path_).NormalizePathSeparatorsTo('/');
 }
 
 void BuildSettings::ItemDefined(std::unique_ptr<Item> item) const {
   DCHECK(item);
   if (!item_defined_callback_.is_null())
     item_defined_callback_.Run(std::move(item));
 }