constructor(pgpMessage) {
    super();

    /**
     * The encrypted PGP message that needs to be decrypted and displayed to
     * the user.
     * @type {string}
     * @private
     */
    this.pgpMessage_ = pgpMessage;

    /**
     * The communication channel with the extension.
     * @type {Port}
     * @private
     */
    this.port_ = null;
  }
@param {string} pgpMessage The encrypted PGP message that needs to be
    decrypted and displayed to the user.