getSelectTenantUiShownCallback() {
    return /** @type {?function()} */ (
        this.getCallbacks_()['selectTenantUiShown'] || null);
  }
Returns the selectTenantUiShown callback. It is triggered when the
select provider UI is shown.
@return {?function()} The selectTenantUiShown callback, null if not
    available.