tools/gn: Convert for loops to use the new range-based loops in C++11.

tools/gn/generate_test_gn_data.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 <fstream>
 #include <iostream>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 12 matching lines @@
 std::string FilePathToUTF8(const base::FilePath& path) {
 #if defined(OS_WIN)
   return base::WideToUTF8(path.value());
 #else
   return path.value();
 #endif
 }
 
 base::FilePath RepoPathToPathName(const std::vector<int>& repo_path) {
   base::FilePath ret;
-  for (size_t i = 0; i < repo_path.size(); i++) {
-    ret = ret.Append(UTF8ToFilePath(base::IntToString(repo_path[i])));
+  for (const auto& elem : repo_path) {
+    ret = ret.Append(UTF8ToFilePath(base::IntToString(elem)));
   }
   return ret;
 }
 
 std::string TargetIndexToLetter(int target_index) {
   char ret[2];
   ret[0] = static_cast<char>('a' + target_index);
   ret[1] = 0;
   return ret;
 }
 
 std::string RepoPathToTargetName(const std::vector<int>& repo_path,
                                  int target_index) {
   std::string ret;
   for (size_t i = 0; i < repo_path.size(); i++) {
     if (i != 0)
       ret.push_back('_');
     ret.append(base::IntToString(repo_path[i]));
   }
   ret += TargetIndexToLetter(target_index);
   return ret;
 }
 
 std::string RepoPathToFullTargetName(const std::vector<int>& repo_path,
                                  int target_index) {
   std::string ret;
-  for (size_t i = 0; i < repo_path.size(); i++) {
+  for (const auto& elem : repo_path) {
     ret.push_back('/');
-    ret.append(base::IntToString(repo_path[i]));
+    ret.append(base::IntToString(elem));
   }
 
   ret += ":" + RepoPathToTargetName(repo_path, target_index);
   return ret;
 }
 
 void WriteLevel(const std::vector<int>& repo_path,
                 int spread,
                 int max_depth,
                 int targets_per_level,
@@ skipping 42 matching lines @@
   }
 }
 
 int main() {
   WriteLevel(std::vector<int>(), 5, 4, 3, 50);  // 781 files, 2343 targets
   //WriteLevel(std::vector<int>(), 6, 4, 2, 50);
   std::cout << "Wrote " << files_written << " files and "
             << targets_written << " targets.\n";
   return 0;
 }