constructor(opt_label, opt_domHelper) {
    super(opt_domHelper);

    /**
     * The label to display.
     * @type {string}
     * @private
     */
    this.initialLabel_ = opt_label || 'Click Me';

    /**
     * The current color.
     * @type {string}
     * @private
     */
    this.color_ = 'red';

    /**
     * Keyboard handler for this object. This object is created once the
     * component's DOM element is known.
     *
     * @type {goog.events.KeyHandler?}
     * @private
     */
    this.kh_ = null;
  }
@param {string=} opt_label A label to display. Defaults to "Click Me" if
    none provided.
@param {goog.dom.DomHelper=} opt_domHelper DOM helper to use.