Exclude memory reducing scenarios and apply minimum percentage to absolute
sizes wrt. capacity rather then relative survival rate.

R=ulan@chromium.org
BUG=chromium:693413

Change-Id: I30cac99a2ce72227e269d72f52a459d4be6234a5
Reviewed-on: https://chromium-review.googlesource.com/445737Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43346}