Replace more for loops in GN

tools/gn/input_conversion.cc

Index: tools/gn/input_conversion.cc
diff --git a/tools/gn/input_conversion.cc b/tools/gn/input_conversion.cc
index 2534f4d8410f21adf8ac669159ff911853d1a544..6369d2dbfa1e7accb8f43a1d8ae0d8f4b13eb0c0 100644
--- a/tools/gn/input_conversion.cc
+++ b/tools/gn/input_conversion.cc
@@ -105,8 +105,8 @@ Value ParseList(const std::string& input, const ParseNode* origin, Err* err) {
     as_lines.resize(as_lines.size() - 1);
 
   ret.list_value().reserve(as_lines.size());
-  for (size_t i = 0; i < as_lines.size(); i++)
-    ret.list_value().push_back(Value(origin, as_lines[i]));
+  for (const auto& line : as_lines)
+    ret.list_value().push_back(Value(origin, line));
   return ret;
 }