class Subgraph {
   public:
    // Creates a graph to build the subgraph in, if it doesn't already exist,
    // using the same op registry and versions as graph_in.
    Node* MakeNodeImage(const Graph* graph_in, Node* node);

    // Returns the graph the subgraph is being built in.
    Graph* GetGraph() const;

    // Builds a FunctionDef, and adds it to 'library'. The value of the