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This reverts commit 1638e067.

Reason for revert: New tests are flaky and causing problems when submitting code.

Original change's description:
> [heap] Do not revive WeakMember during incremental marking
> 
> Overwriting deleted values with cleared values potentially revives
> buckets in collections. For atomic garbage collections this is not a
> problem as those values are filered out in the visitors already. For
> incremental garbage collections the deleted values may be introduced by
> erasing a value from a container after it has been visited by the
> incremental marker.
> 
> Bug: chromium:870196, chromium:757440
> Change-Id: I1d628f00c2e2ea6e36e880d50a397dcbcc8566d1
> Reviewed-on: https://chromium-review.googlesource.com/1164950
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Reviewed-by: Keishi Hattori <keishi@chromium.org>
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#581238}

TBR=haraken@chromium.org,keishi@chromium.org,mlippautz@chromium.org

Change-Id: I632b5594d137acd37b4639ebcd46f8d61638dbc0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:870196, chromium:757440
Reviewed-on: https://chromium-review.googlesource.com/1165328Reviewed-by: Fredrik Hubinette <hubbe@chromium.org>
Commit-Queue: Fredrik Hubinette <hubbe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581277}