Currently, it fails:

In file included from ../../chromeos/services/secure_channel/public/mojom/secure_channel_mojom_traits_unittest.cc:9:
../../mojo/public/cpp/test_support/test_utils.h:19:38: error: no member named 'SerializeAsMessage' in 'chromeos::secure_channel::mojom::ConnectionPriority'
  mojo::Message message = MojomType::SerializeAsMessage(input);
                          ~~~~~~~~~~~^
../../chromeos/services/secure_channel/public/mojom/secure_channel_mojom_traits_unittest.cc:23:21: note: in instantiation of function template specialization 'mojo::test::SerializeAndDeserialize<chromeos::secure_channel::mojom::ConnectionPriority, chromeos::secure_channel::ConnectionPriority>' requested here
        mojo::test::SerializeAndDeserialize<
                    ^
In file included from ../../chromeos/services/secure_channel/public/mojom/secure_channel_mojom_traits_unittest.cc:9:
../../mojo/public/cpp/test_support/test_utils.h:26:21: error: no member named 'DeserializeFromMessage' in 'chromeos::secure_channel::mojom::ConnectionPriority'
  return MojomType::DeserializeFromMessage(std::move(message), output);
         ~~~~~~~~~~~^
2 errors generated.