_setupOverlayCtrl() {
    super._setupOverlayCtrl();

    this.__datepickerBeforeShow = () => {
      this._overlayCtrl.updateConfig(this._defineOverlayConfig());
    };
    this._overlayCtrl.addEventListener('before-show', this.__datepickerBeforeShow);
  }
Subclassers can replace this with their custom extension invoker icon