public function getUserGroupsThatCanViewArtifact(Tracker_Artifact $artifact)
 {
     $authorized_ugroups = array(ProjectUGroup::PROJECT_ADMIN);
     $artifact_ugroup_ids = $artifact->getAuthorizedUGroups();
     if ($artifact_ugroup_ids) {
         $authorized_ugroups = array_merge($authorized_ugroups, $artifact_ugroup_ids);
     }
     return array_unique($authorized_ugroups);
 }