In crrev.com/c/3056970 I merged reporting allocated bytes from CppHeap
to v8 with reporting from cppgc to CppHeap. The reporting handler
assumed in_no_gc_scope() is false.
Unfortunately this breaks. On heap termination, cppgc will report to
CppHeap but CppHeap will have entered a no gc scope when it detached
from the isolate.

We could adjust the DCHECK, but I think it's simpler to revert to the
previous unmerged state and simply port the bug fix from
crrev.com/c/3056970 (i.e. lines 484-486 in cpp-heap.cc in this CL).

Bug: chromium:1056170
Change-Id: I5aa953c31388f7b3bb3326ff10d5a33961be2aa1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3067227Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76088}