Currently, the InternalGroupBackend suggests all known groups. Update
it to only return results that are visible to the CurrentUser. The
LdapGroupBackend only returns suggestions for groups the user is
a member of, so it does not require an update. This change was
required because doing membership checks for visibility on a large
number of suggestions that the user was not a member of was slow.
Change-Id: Ic494cf31850b0d473edc437955c07c906ce11711
5660a19d05