Add a control benchmark.

I'm thinking of using this in perf with something like:
   ratio(fill(filter("test=foo")), fill(filter("test=control")))

Does that make sense to you?

Not sure that this is really a good control bench on all bots,
but I propose we just run it a bit and find out if it needs work.

BUG=skia:

Review URL: https://codereview.chromium.org/1129823003
2 files changed