if (obj instanceof Failure) {
        return ((Failure) obj).exception;
      }
    }
    return null;
  }

  /**
   * If this future has been cancelled (and possibly interrupted), cancels (and possibly interrupts)
   * the given future (if available).
   */
  final void maybePropagateCancellationTo(@CheckForNull Future<?> related) {
    if (related != null & isCancelled()) {

   * X-DNS-Prefetch-Control}</a> header controls DNS prefetch behavior. Value can be "on" or "off".
   * By default, DNS prefetching is "on" for HTTP pages and "off" for HTTPS pages.
   */
  public static final String X_DNS_PREFETCH_CONTROL = "X-DNS-Prefetch-Control";
  /**
   * The HTTP <a href="http://html.spec.whatwg.org/multipage/semantics.html#hyperlink-auditing">