Every page that can be accessed concurrently during marking needs to be
synced to avoid data races with page alloation. TraceTrait for mixins
uses the object start bitmap of a page and thus requires a sync.

Bug: chromium:10561670
Change-Id: Ia26be973019dcd1d9f7650cc139b16369d515df6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2783023Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73623}