The field is updated on the main thread and read on threads using
LocalHeap to possibly trigger GC in fuzzing configurations.

Bug: chromium:1286699
Change-Id: I15330b7542358ce1a2307a1f258655126b252c03
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3383776Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78591}