if (!status.ok()) {
    done(status);
  }
}

class TpuNodeDeviceFactory : public DeviceFactory {
 public:
  Status ListPhysicalDevices(std::vector<string>* devices) override;
  Status CreateDevices(const SessionOptions& options, const string& name_prefix,
                       std::vector<std::unique_ptr<Device>>* devices) override;
};

Status TpuNodeDeviceFactory::ListPhysicalDevices(std::vector<string>* devices) {