concurrent sweeping is disabled, which is not correct.

MemoryAllocator: :CanFreeMemoryChunk returns true for the case when
Change-Id: I560bac0275473445b52fba28b5e647b54f523a3a
Reviewed-on: https://chromium-review.googlesource.com/528081Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45792}