GitLab

Add the initial benchmark, which measures double privacy budget UKM
serialization performance.

Bug: 973801
Change-Id: I90403af701246cf8575681c0789b2344622b1261
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2075477
Commit-Queue: Caleb Raitto <caraitto@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745631}