GitLab

Makes the middle slot promo Finch-configurable. Flag is enabled by
default.

Bug: 1166869
Change-Id: If6d4e06577f99b635f04fbe406334b66f62210b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2638934
Commit-Queue: Esmael Elmoslimany <aee@chromium.org>
Reviewed-by: Esmael Elmoslimany <aee@chromium.org>
Auto-Submit: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845381}