$userListCriterion = new CriterionUserList();
$userListCriterion->setUserListId($userListId);
// Create biddable ad group criterion.
$adGroupCriterion = new BiddableAdGroupCriterion();
$adGroupCriterion->setAdGroupId($adGroupId);
$adGroupCriterion->setCriterion($userListCriterion);
// Create an ad group criterion operation and add it to the list.
$operation = new AdGroupCriterionOperation();
$operation->setOperand($adGroupCriterion);
$operation->setOperator(Operator::ADD);
$operations[] = $operation;