function getNativeUserAgentData() {
  const navigator = getNavigator();
  // TODO(user): Use navigator?.userAgent ?? null once it's supported.
  if (navigator) {
    return navigator.userAgentData || null;
  }
  return null;
}
Gets the native userAgentData object from navigator if it exists.
If navigator.userAgentData object is missing returns null.
@return {?NavigatorUAData}