Conceptually, Oilpan uses tri-color marking even though the
implementatin only uses a single mark bit. The difference between gray
and black is represented by the fact that an objet is contained within
a worklist.

Live bytes are accounted on gray->black transition and must only
happen once. This is generally implemented when retrieving an object
from the work list and processing it.

For weak containers this CL fixes the following issues:

1. Weak containers that are strongified during stack scanning were
   double accounted as they were just added to the marking worklist.
   Instead, directly process them during stack scanning.
2. Accounting was missing in case of purely weak collections without
   ephemeron tracing. In such a case, the backing store would not be
   added to a worklist and be considered as black immediately. The fix
   is to directly account the marked bytes in such a scenario.

Bug: chromium:1056170
Change-Id: I350ae1b90ad1753d024a3ce33fc3ec3126a2095d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2900661Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74629}