setKeyringEncrypted(encrypted) {
    var button =
        this.getElementByClass(constants.CssClass.KEYRING_PASSPHRASE_CHANGE);
    button.textContent = encrypted ?
        chrome.i18n.getMessage('keyMgmtChangePassphraseLabel') :
        chrome.i18n.getMessage('keyMgmtAddPassphraseLabel');
  }
Updates the button to set the keyring's passphrase according to whether the
keyring is encrypted or not.
@param {boolean} encrypted True if the keyring is encrypted.