onToggleKeydown(e) {
    switch (e.code) {
      case 'ArrowUp':
        e.preventDefault();
        this.open(this._getPreviousMenuItem());
        break;
      case 'ArrowDown':
      case 'Enter':
      case ' ':
        e.preventDefault();
        this.open(this._getNextMenuItem());
        break;
      default:
       // no op
    }
  }
Handler for tool button.
@param {KeyboardEvent} e