SimulateIncrementalMarking needs to invoke EnsureSweepingCompleted in
a safepoint. Otherwise RefillFreeList in this method races with
concurrent allocation.

Bug: v8:10315
Change-Id: I9aa11d225a1c1844648788f956fd72988fe269fe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2349299Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69336}