The callback is useful to embedders to trigger various actions such as
recomputing live set.

Bug: chromium:1056170
Change-Id: I7d80b9b768a728e23303f945e416df97fd9b7805
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2173358
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67532}