PartitionAlloc: PCScan: Commit quarantine bitmaps only when needed

Bug: 11297512
Change-Id: I4d09c4705105e8ba66bbb4282cecebf2b33e56f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2517351


Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824821}