pathFromGoogleStorageUrl function
Returns a path from a given gs:// URL.
If no path exists, the root path will be returned.
Implementation
String pathFromGoogleStorageUrl(String url) {
  assert(url.startsWith('gs://'));
  int stopIndex = url.indexOf('/', 5);
  if (stopIndex == -1) return '/';
  return url.substring(stopIndex + 1, url.length);
}