This allows handling transitions arrays in concurrent marking

Bug: chromium:694255
Change-Id: I28196fccbf03bfba7d7dada1884813be372ddb54
Reviewed-on: https://chromium-review.googlesource.com/610961
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47303}