inline bool IsNextIteration(const NodeDef& node_def) {
  return node_def.op() == "NextIteration" ||
         node_def.op() == "RefNextIteration";
}
inline bool IsNextIteration(const NodeDef& node_def) {
  return node_def.op() == "NextIteration" ||
         node_def.op() == "RefNextIteration";
}