long estimatedSize = 0L;
    ImmutableList.Builder<Spliterator.OfLong> splitrsBuilder =
        new ImmutableList.Builder<>(streams.length);
    for (LongStream stream : streams) {
      isParallel |= stream.isParallel();
      Spliterator.OfLong splitr = stream.spliterator();
      splitrsBuilder.add(splitr);
      characteristics &= splitr.characteristics();

     */
    @IgnoreJRERequirement // Users will use this only if they're already using streams.
    @CanIgnoreReturnValue
    public Builder addAll(LongStream stream) {
      Spliterator.OfLong spliterator = stream.spliterator();
      long size = spliterator.getExactSizeIfKnown();
      if (size > 0) { // known *and* nonempty
        ensureRoomFor(Ints.saturatedCast(size));
      }