Replace the second level visitation with a much simpler logic that
just separately dispatches the special cases. All other cases can
use a dispatch that just evacuates an object based on size.

This is similar to the logic used in the mark-compact collector. The
goal is to align behaviors as much as possible, highlighting and 
fixing performance issues in the different behaviors.

This CL is mechanical as possible. A followup will clean
up the naming scheme and dispatching.

Bug: chromium:738368
Change-Id: Ia5a426c5ebb25230000b127580c300c97cff8b1b
Reviewed-on: https://chromium-review.googlesource.com/558060
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46364}