Follow up for T181829. No direct means to access the "userName" (which is the 4th parameter to the UserGroupMembership::getLink()) which exceeds the scope of GCI.
Per discussion with @Bawolff, the userName can be gotten via
17:00 < bawolff> So the correct fix is to make GlobalUsersPager::getUserGroups() to take another parameter
16:59 < bawolff> Anyways, GlobalUsersPager::formatRow calls GlobalUsersPager::getUserGroups
So we approved T181829 on GCI and created the follow up.