Modify internal signature to be more flexible.
Modify internal signature to be more flexible.

It's conceivable that we'd want to be able to ask whether an
arbitrary user is in a group, not just the current one.

Change-Id: Ib0a49706e6a3b5f89520e2a77f3111456e842851

jmorse/cyanide,jmorse/cyanide,jmorse/cyanide,jmorse/cyanide