private function setCurlErrorFromUrlFetchError($urlfetch_error,
                                                 $urlfetch_message) {
    if (array_key_exists($urlfetch_error, self::$urlfetch_curl_error_map)) {
      $this->setError(self::$urlfetch_curl_error_map[$urlfetch_error],
                      $urlfetch_message);
    } else {
      $this->setError(-1, $urlfetch_message);  // Maps to "Unknown Error".
    }
  }