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

tools/gn/substitution_pattern.cc

Index: tools/gn/substitution_pattern.cc
diff --git a/tools/gn/substitution_pattern.cc b/tools/gn/substitution_pattern.cc
index 60ec191bcc0681fa7cb953815e84441ce64c8b01..838a5a7a471449471629d7f59695a800d1c06320 100644
--- a/tools/gn/substitution_pattern.cc
+++ b/tools/gn/substitution_pattern.cc
@@ -101,19 +101,19 @@ SubstitutionPattern SubstitutionPattern::MakeForTest(const char* str) {
 
 std::string SubstitutionPattern::AsString() const {
   std::string result;
-  for (size_t i = 0; i < ranges_.size(); i++) {
-    if (ranges_[i].type == SUBSTITUTION_LITERAL)
-      result.append(ranges_[i].literal);
+  for (const auto& elem : ranges_) {
+    if (elem.type == SUBSTITUTION_LITERAL)
+      result.append(elem.literal);
     else
-      result.append(kSubstitutionNames[ranges_[i].type]);
+      result.append(kSubstitutionNames[elem.type]);
   }
   return result;
 }
 
 void SubstitutionPattern::FillRequiredTypes(SubstitutionBits* bits) const {
-  for (size_t i = 0; i < ranges_.size(); i++) {
-    if (ranges_[i].type != SUBSTITUTION_LITERAL)
-      bits->used[static_cast<size_t>(ranges_[i].type)] = true;
+  for (const auto& elem : ranges_) {
+    if (elem.type != SUBSTITUTION_LITERAL)
+      bits->used[static_cast<size_t>(elem.type)] = true;
   }
 }