constructor(confirmationResult, errorHandler) {
    /**
     * @const @private {!firebase.auth.ConfirmationResult} The confirmation
     *     result from a phone number sign-in or link.
     */
    this.confirmationResult_ = confirmationResult;
    /**
     * @const @private {function(*):*} The error handler for confirm method.
     *     If not provided, the error will be rethrown.
     */
    this.errorHandler_ = errorHandler || (error => {throw error;});
    /** @const {string} The verification ID in confirmation result. */
    this.verificationId = confirmationResult['verificationId'];
  }
@param {!firebase.auth.ConfirmationResult} confirmationResult The
    confirmation result from phone Auth.
@param {(function(!Error):!goog.Promise)=} errorHandler The error
    handler for confirm method.