PagedSpace::CommittedPhysicalMemory() needs to use mutex when iterating
chunks due to concurrent allocations.

Also reorder sampling of memory statistics according to this order:

1) used memory
2) committed physical memory
3) committed memory

That way, used <= committed physical <= committed should hold.

Bug: v8:10315
Change-Id: Ie922ecc4846f724a09c71667a898bf74a8652220
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2390768
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69698}