Unfortunately, this isn't using DI completely, because of the
User::newSystemUser call. I'm not even sure if we really need to call it
or we can just stick to new UserIdentityValue, but leaving like this for
now.
Also, the types were weakened to UserIdentity, so the transition is
going to be easy anyway.
Change-Id: I08f8fae0fcc622ff0ac3f86771476d06d1c18549
