new Throwable("Failure occurred while trying to finish a future.") {
              @Override
              public synchronized Throwable fillInStackTrace() {
                return this; // no stack trace
              }
            });
    final Throwable exception;

    Failure(Throwable exception) {
      this.exception = checkNotNull(exception);
    }
  }

   * a request itself.
   *
   * @since 31.0
   */
  public static final String X_DEVICE_REQUESTED_WITH = "X-Device-Requested-With";
  /** The HTTP {@code X-Do-Not-Track} header field name. */
  public static final String X_DO_NOT_TRACK = "X-Do-Not-Track";
  /** The HTTP {@code X-Forwarded-For} header field name (superseded by {@code Forwarded}). */
  public static final String X_FORWARDED_FOR = "X-Forwarded-For";

              [INFO] Validating units:
              [INFO]    Ignored 53 units with compilation errors in first pass.
              [INFO] Compile with -strict or with -logLevel set to TRACE or DEBUG to see all errors.

            Turning up the log level, we see that GWT is trying to compile classes from other
            packages, like RangeTest. The reason for this is that GWT doesn't distinguish between

    @CheckForNull private Iterator<? extends T> toRemove;

    /* The iterator currently returning elements. */
    private Iterator<? extends T> iterator;

    /*
     * We track the "meta iterators," the iterators-of-iterators, below.  Usually, topMetaIterator
     * is the only one in use, but if we encounter nested concatenations, we start a deque of