 used in submission. Note that `serialize`
       * is a Polymer reserved keyword, so calling `someIronForm`.serialize()`
       * will give you unexpected results.
       * @return {Object} An object containing name-value pairs for elements that
       *                  would be submitted.
       */
      serializeForm: function() {
        // Only elements that have a `name` and are not disabled are submittable.
        var elements = this._getSubmittableElements();
        var json = {};
        for (va