The reduer should only fire on increasing memory.

R=ulan@chromium.org

Change-Id: I4abd956ea14730b223724a01af819be574b1aa3a
Reviewed-on: https://chromium-review.googlesource.com/c/1308354Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57149}