The new scheduling reduces the main thread marking performed in
tasks and on allocation. It is based on two counters:
- bytes_marked,
- scheduled_bytes_to_mark.

The bytes_marked accounts marking done both the main thread and
the concurrent threads. The scheduled_bytes_to_mark increases based
on allocated bytes and also based on time passed since the start
of marking. The main thread steps are allowed to mark the minimal
amount if bytes_marked is greater than scheduled_bytes_to_mark.

This also changes tasks posted for marking. Before only normal
tasks were posted. Now delayed tasks are posted if the marker is
ahead of schedule.

Bug: 926189

Change-Id: I5bc9c33a5ecfc9f8d09f78d08ae277d16a2779ca
Reviewed-on: https://chromium-review.googlesource.com/c/1443056
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59433}