f (this.allowRedirect) {
          // If we're submitting the form natively, then create a hidden element for
          // each of the values.
          for (var element in json) {
            this.$.helper.appendChild(this._createHiddenElement(element, json[element]));
          }

          // Copy the original form attributes.
          this.$.helper.action = this._form.getAttribute('action');
          this.$.helper.method = this._form.getAttribute('method') || 'GET';
          this.$.helper.contentType