function checkNewKeys(intlClass, checkKey) {
  const newKeyInfo = newlySupportedKeys.get(intlClass);
  if (newKeyInfo) {
    for (let index in newKeyInfo) {
      const newKey = newKeyInfo[index];
      if (newKey.browser && newKey.key === checkKey &&
          browser.isVersionOrHigher(newKey.minVersion)) {
        return true;
      }
    }
  }
  return false;
}
Check if an option is a newly defined key that is not yet
in the externs/intl.js file.
@param {typeof Intl.NumberFormat|typeof Intl.PluralRules|typeof
    Intl.DateTimeFormat|typeof Intl.ListFormat|typeof
    Intl.RelativeTimeFormat} intlClass
@param {string} checkKey
@return {boolean} true if the key is already available.