The flag was not used anymore and any CollectGarbage call will finalize
marking.

Change-Id: I29ee60b187c9038acc4b42b8334546498f54f117
Reviewed-on: https://chromium-review.googlesource.com/1228013Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56018}