public function deleteChart($renderer, $id, $user_can_update_report)
 {
     $ok = false;
     $session = new Tracker_Report_Session($renderer->report->id);
     $session->changeSessionNamespace("renderers.{$renderer->id}");
     if (isset($session->charts[$id])) {
         $session->set("charts.{$id}", 'removed');
         $session->setHasChanged();
     } else {
         if ($user_can_update_report) {
             $this->deleteDb($renderer, $id);
         }
     }
 }