This is a follow-up for 8ed81dde.

The TSAN exception has to be in MarkObject because that is called from
two places in concurrent marking.

Bug: v8:7574
Change-Id: If36b564bce0970c9b44c029055114bb6e2a74059
Reviewed-on: https://chromium-review.googlesource.com/973526
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52157}