Scavenger and full MC now rely on the same allocation behavior for their
evacuation.

Bug: 
Change-Id: Iddb0affe171187308e5b77ab0d3cfa75211bd8b8
Reviewed-on: https://chromium-review.googlesource.com/575983Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46781}