%SimulateFullSpace uses PauseAllocationObserversScope internally and
so does a GC. When there happens to be a GC during %SimulateFullSpace
(caused by --stress-concurrent-allocation here), then the DCHECK in
AllocationCounter::Pause would fail because it was already paused.

Solve this by counting the number of active
PauseAllocationObserversScopes.

Bug: v8:11936
Change-Id: I86487c24fd33739fd7e6635501b5f0257806c4bc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2992727Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75446}