GitLab

This will allow us to measure the performance difference and see
the difference in the user engagement metrics and extrapolate to
estimate the usefulness of bfcache.

One-pager:
https://docs.google.com/document/d/10Ff_5oq7k-oYuXTTKdN0v_JKG3bU1GPgAWWF7i4nMvs/edit#

R=creis@chromium.org
BUG=954271

Change-Id: Id31309a9e4926073b10b0e983ed193cf207ec9f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574798
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652435}