    } else {
        this.addEventListener('input', this._onInput);
      }

      // Only validate when attached if the input already has a value.
      if (this._inputElementValue != '') {
        this._handleValueAndAutoValidate(this._inputElement);
      } else {
        this._handleValue(this._inputElement);
      }
    },

    _onAddonAttached: function(event) {
      if (!this._addons) {
        this._addons = [];
      }
      var target = event.target;
      if (this._addons.indexOf(target) === -1)