[perf] Return error on unknown algorithm
[perf] Return error on unknown algorithm

This might be failing on an unknown algorithm, like the man whitney U test.

Change-Id: I0e8d12addca716e1d91b4a7c9a50edc1ea766cb2
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/337173
Reviewed-by: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot