We already filter out fillers in ProcessMarkingDeque.

BUG=

Change-Id: Iee0dbfffe6e4eb5c65a1c25ba75c4c69bf15355b
Reviewed-on: https://chromium-review.googlesource.com/453481Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43754}