updateKeyringPassphrase_() {
    var passphrases = goog.array.map(
        this.getElementsByClass(constants.CssClass.PASSPHRASE), function(elem) {
          return elem.value;
        });

    if (this.hasMatchingPassphrases_(passphrases)) {
      this.showKeyringMgmtForm_(constants.ElementId.KEYRING_OPTIONS_DIV);
      this.updatePassphraseCallback_(passphrases[0]);
    } else {
      window.alert(chrome.i18n.getMessage('keyMgmtPassphraseMismatchLabel'));
      // Show the form again to create listeners and clear the input.
      this.showKeyringMgmtForm_(
          constants.ElementId.KEYRING_PASSPHRASE_CONFIRM_DIV);
    }
  }
Handles requests from the user to update the keyring's passphrase.
@private