renderPassphraseCallback_(uid) {
    var result = new e2e.async.Result();
    var popupElem = goog.dom.getElement(constants.ElementId.CALLBACK_DIALOG);
    var dialog = new dialogs.Generic(
        chrome.i18n.getMessage('promptPassphraseCallbackMessage', uid),
        function(passphrase) {
          goog.dispose(dialog);
          result.callback(/** @type {string} */ (passphrase));
        },
        // Use a password field to ask for the passphrase.
        dialogs.InputType.SECURE_TEXT, '',
        chrome.i18n.getMessage('actionEnterPassphrase'),
        chrome.i18n.getMessage('actionCancelPgpAction'));

    this.addChild(dialog, false);
    dialog.render(popupElem);
    return result;
  }
Renders the UI elements needed for requesting the passphrase of an
individual PGP key.
@param {string} uid The UID of the PGP key.
@return {!e2e.async.Result<string>} A promise resolved with the
    user-provided passphrase.
@private