--incremental-marking-soft-trigger is a percentage of (limit - size)
at which incremental marking starts via a task.

--incremental-marking-hard-trigger is a percentage of (limit - size)
at which incremental marking starts immediately.

E.g. --incremental-marking-soft-trigger=50 and
--incremental-marking-soft-trigger=100 will start a task half-way to
the limit and start incremental marking at the limit.

Change-Id: I14be992c8552dc47de401b376b815f693564cb74
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144069Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67140}