filterFn = function(node) {
    if (!(node instanceof lf.proc.SelectStep)) {
      return false;
    }

    var predicate = queryContext.getPredicate(node.predicateId);
    return predicate instanceof lf.pred.CombinedPredicate &&
        predicate.operator == lf.pred.Operator.OR;
  }
@param {!lf.query.Context} queryContext
@return {!Array<!lf.proc.SelectStep>} Finds SelectStep instances in the tree
    corresponding to OR predicates.
@private