When black allocation is turned on at deserialization time, then
slots in deserialized objects have to be visited by the incremental
marker. For spaces with reservations, this has always been done; for
large object space with its special handling, this patch adds it.

Additionally, we must ensure that no incremental steps that might
cause incremental marking to finish are performed while there is an
AlwaysAllocateScope around.

BUG=chromium:718859

Review-Url: https://codereview.chromium.org/2868103002
Cr-Commit-Position: refs/heads/master@{#45231}