The heuristic is no longer needed now that we have concurrent marking.

Bug: chromium:834371
Change-Id: I8ca3eaacdab618f690d8007aff66713260ace19f
Reviewed-on: https://chromium-review.googlesource.com/1017123Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52693}