updateNotification_() {
    if (this.notificationCount_) {
      if (this.getCount() === 0) {
        this.countSvgText_.textContent = '!';
        this.countSvg_.setAttribute('opacity', '1');
      } else {
        this.countSvgText_.textContent =
          this.notificationCount_ > 99
            ? '99+'
            : this.notificationCount_.toString();
      }
      this.countSvg_.setAttribute('opacity', '1');
    } else {
      this.countSvg_.setAttribute('opacity', '0');
    }
  }
Updates the notification circle icon.
@private