setAnonymousUid(anonymousUid) {
    if (anonymousUid) {
      this.uri_.setParameterValue(
          firebaseui.auth.ActionCodeUrlBuilder.Parameter.ANONYMOUS_UID,
          anonymousUid);
    } else {
      this.uri_.removeParameter(
          firebaseui.auth.ActionCodeUrlBuilder.Parameter.ANONYMOUS_UID);
    }
  }
Sets the UID of the anonymous user to upgrade.
@param {?string} anonymousUid The anonymous user to upgrade.