Overrides SelectQueryExtender::__construct
public function __construct(SelectQueryInterface $query, DatabaseConnection $connection) {
  parent::__construct($query, $connection);
  // Add convenience tag to mark that this is an extended query. We have to
  // do this in the constructor to ensure that it is set before preExecute()
  // gets called.
  $this
    ->addTag('tablesort');
}