message: Add comments about arg_nodes and ret_nodes in FunctionBody
diff: @@ -72,7 +72,11 @@ struct FunctionBody {
  Graph* graph = nullptr; // owned.
  DataTypeVector arg_types;
  DataTypeVector ret_types;
  + // arg_nodes[i] contains the i'th function input. In other words,
  + // GetNodeAttr(arg_nodes[i]->attrs(), "index") == i.
  gtl::InlinedVector<Node*, 4> arg_nodes;
  + // ret_nodes[i] contains the i'th function output. In other words,
  + // GetNodeAttr(ret_nodes[i]->attrs(), "index") == i.
  gtl::InlinedVector<Node*, 4> ret_nodes;
  gtl::InlinedVector<Node*, 4> control_ret_nodes;
  