OldGenerationAllocationCounter() needs to be invoked in safepoint,
otherwise invocation races with background threads incrementing the
counter.

Bug: v8:10315
Change-Id: Iab005582bab7ebf63e7a5a796b25690f499a99eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2235544
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68250}