setProviderId(providerId) {
    if (providerId) {
      this.uri_.setParameterValue(
          firebaseui.auth.ActionCodeUrlBuilder.Parameter.PROVIDER_ID,
          providerId);
    } else {
      this.uri_.removeParameter(
          firebaseui.auth.ActionCodeUrlBuilder.Parameter.PROVIDER_ID);
    }
  }
Sets the provider ID of the credential to link.
@param {?string} providerId The provider ID of the credential to link.