The last allocated large object in the young generation is not
guaranteed to be initialized when the concurrent marker visits it.

This patch adds a mechanism for the concurrent marker to put such
objects on the on-hold worklist similar to how new space objects are
handled.

Bug: chromium:852420
Change-Id: I749e9a7f3dcee6f177f4d95980a4f693c0fd4b04
Reviewed-on: https://chromium-review.googlesource.com/c/1454916Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59377}