getRefs = function(info, tableName, opt_constraintAction) {
    var refs = info.getReferencingForeignKeys(tableName, opt_constraintAction);
    return refs === null ? null : refs.map(function(ref) {
      return ref.name;
    });
  }
@param {!lf.schema.Info} info
@param {string} tableName
@param {!lf.ConstraintAction=} opt_constraintAction
@return {?Array<string>}