The new flag controls foreground incremental marking tasks and does not
affect background concurent marking tasks.

Change-Id: I46bda6b10c76b7a7f2ed2e123afe85bc04935624
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2135733Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66988}