Add nanobench, a fresh look at our microbenchmark harness.

out/Release/nanobench runs 4-5x faster on my Z620 and ~2x faster on my N5 than out/Release/bench with the same configs.

(Debug isn't really comparable.  I haven't added the Debug -> single loop check.)

BUG=skia:
R=djsollen@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/347443002
4 files changed