add missing unit test for 128-bit ops

Change-Id: I233398bf34411231d44613d89aed28935fe30a28
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/340796
Commit-Queue: Herb Derby <herb@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
1 file changed