Since the benchmark is very fast, a warmup is useful to reduce the noise
created by optimization.

Change-Id: I4902c5c1695099be766d0fcc563c2f5d0892d3a9
Reviewed-on: https://chromium-review.googlesource.com/1204112
Commit-Queue: Hai Dang <dhai@google.com>
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55618}