isRegistered is part of the slick UserIdentity interface, i.e.
it's the more "canonical" form. This change makes it a bit
easier to move away from using the huge (4000+ LOC) User class
everywhere, in favor of the UserIdentity interface, where
possible.
This patch is meant as a small step towards this goal. I tried
to replace some usages of User type hints already, but prefer
to go in small, incremental steps.
Change-Id: I039c7a18672dfb6ea9507752bce9ea754babd690
The nicer approach would be setting the parameter default to [],
but that breaks ApiSandbox.
Bug: T254699
Change-Id: I6c553e27248ff7d6c696f116cb34eb238dade440