* fail. If it is too short, slow connections will be marked as failed and extra TCP and TLS
   * handshakes will be required.
   *
   * The deadline is currently hardcoded. We may make this configurable in the future!
   */
  internal fun sendDegradedPingLater() {
    this.withLock {
      if (degradedPongsReceived < degradedPingsSent) return // Already awaiting a degraded pong.
      degradedPingsSent++