    event.preventDefault();
        }

        // If you've called this before distribution happened, bail out.
        if (!this._form) {
          return;
        }

        if (!this.validate()) {
          this.fire('iron-form-invalid');
          return;
        }

        // Remove any existing children in the submission form (from a previous submit).
        this.$.helper.textContent = '';

        var json = this.serializeForm();

        // If we want a redirect, submit the form natively.
        i