// CustomDeviceOpHandler.
  virtual absl::Status RegisterCustomDevice(
      const string& name, std::unique_ptr<CustomDevice> device) = 0;

  // Return FunctionLibraryDefinition. Transformations need to use it to use it
  // to invoke MLIR compiler passes.
  virtual FunctionLibraryDefinition* FuncLibDef() = 0;

  // Resets the global rendezvous used for functions.
  virtual void ResetGlobalRendezvousForFunction() = 0;

                   const tensorflow::ConfigProto& config_proto,
                   const FunctionOptions& function_options,
                   std::unique_ptr<tensorflow::Graph>* graph,
                   tensorflow::FunctionLibraryDefinition* flib_def,
                   std::vector<std::string>* control_ret_node_names,
                   bool* control_rets_updated) override {
    // Inject failure to function instantiation if finding a node that contains