GitLab

This reverts commit 31f93aa2.

Reason for revert: 

Findit found this CL as the culprit for failed wtf_unittests in builds:
- https://ci.chromium.org/p/chromium/builders/ci/Linux%20MSan%20Tests/21982
- https://ci.chromium.org/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests/17513

Sample analysis: https://findit-for-me.appspot.com/waterfall/failure?redirect=1&url=https://ci.chromium.org/p/chromium/builders/ci/Linux%20MSan%20Tests/21982


Original change's description:
> heap: Check empty or deleted keys on local copy
> 
> Tracing an HashTable involves checking whether keys are empty or
> deleted. This can result in data races with the mutator if the
> HashTable is modified while it is traced.
> To avoid such data races, we create a local copy of the key on the
> concurrent thread and perform the check on the copy.
> 
> Using the local copy on the mutator thread would result in significant
> regressions. Measured locally on the facebook_infinite_scroll:2018 story
> from v8.browsind_desktop benchmark, showed an increase ranging from 70%
> to 110% in the time it takes to process ephemerons (this measurement
> doesn't cover all HashTables, just the ephemeron HashTable).
> To avoid these regressions, the local copy is used only for concurrent
> visitors.
> 
> For further details see
> https://drive.google.com/open?id=13DTRcF3xfVjJ2QaKzAOYFzqvTfGRNiX6WWL3CCACSoM
> 
> Bug: 986235
> Change-Id: Ie135c1076bd1834ae7f8b97ca6446890fc30a02c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2012961
> Commit-Queue: Omer Katz <omerkatz@chromium.org>
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#735833}

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

Change-Id: I8f0e249f4db3326b38d774c9d718fdcd0a2566f6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 986235
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2025324Reviewed-by: Chan Li <chanli@chromium.org>
Commit-Queue: Chan Li <chanli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735962}