This reverts commit 494068c1.

Reason for revert: https://bugs.chromium.org/p/chromium/issues/detail?id=840282

Original change's description:
> [heap] Clear from space after garbage collection.
>
> Bug: chromium:829771
> Change-Id: I9e71e6cbba347dd6951e5415332e5178df9b5122
> Reviewed-on: https://chromium-review.googlesource.com/1041685
> Commit-Queue: Hannes Payer <hpayer@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52957}

TBR=hpayer@chromium.org,mlippautz@chromium.org

Bug: chromium:829771
Change-Id: I3c36baaf849a7d5dbf48db2ae2178e15b3b886f8
Reviewed-on: https://chromium-review.googlesource.com/1049888
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53079}