skpbench: add "resultsfile" option

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4654

Change-Id: I1a26eddb40de1398cad5348d3fe0ba397a87dbb0
Reviewed-on: https://skia-review.googlesource.com/4654
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed