message: Add missing API to device factory
diff: @@ -48,6 +48,10 @@ class XlaIpuDeviceFactory : public DeviceFactory {
  public:
  Status CreateDevices(const SessionOptions& options, const string& name_prefix,
  std::vector<std::unique_ptr<Device>>* devices) override;
  +
  + virtual Status ListPhysicalDevices(std::vector<string>* devices) override {
  + devices->push_back(absl::StrCat("/physical_device:", DEVICE_XLA_IPU, ":0"));
  + }
  };
  Status XlaIpuDeviceFactory::CreateDevices(
  