Replace more for loops in GN

tools/gn/function_process_file_template.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/functions.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/settings.h"
 #include "tools/gn/substitution_list.h"
 #include "tools/gn/substitution_writer.h"
@@ skipping 80 matching lines @@
     *err = Err(template_arg, "Not a string or a list.");
     return Value();
   }
 
   SubstitutionWriter::ApplyListToSourcesAsString(
       scope->settings(), subst, input_files, &result_files);
 
   // Convert the list of strings to the return Value.
   Value ret(function, Value::LIST);
   ret.list_value().reserve(result_files.size());
-  for (size_t i = 0; i < result_files.size(); i++)
-    ret.list_value().push_back(Value(function, result_files[i]));
+  for (const auto& file : result_files)
+    ret.list_value().push_back(Value(function, file));
 
   return ret;
 }
 
 }  // namespace functions