Previous version:
https://chromium-review.googlesource.com/c/v8/v8/+/1292058

BUG=v8:8179
TBR=hpayer@chromium.org, gsathya@chromium.org

Change-Id: Ia79b75a0630c5926e59206c29053addc88bfb6fe
Reviewed-on: https://chromium-review.googlesource.com/c/1296210Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56886}

This reverts commit 49bd7f50.

Reason for revert: breaks nonintl build since the added string is inside wrong ifdefs

Original change's description:
> [js weak refs] Add WeakCell.clear()
> 
> BUG=v8:8179
> 
> Change-Id: Ic0d9af273a8a92177bf60e4be0dd5bddaf31868c
> Reviewed-on: https://chromium-review.googlesource.com/c/1292058
> Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Marja Hölttä <marja@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56853}

TBR=marja@chromium.org,hpayer@chromium.org,gsathya@chromium.org

Change-Id: I7d6831cfd8a5263ee327c2a80274d1cd10dd65cc
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8179
Reviewed-on: https://chromium-review.googlesource.com/c/1293573Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56855}

BUG=v8:8179

Change-Id: Ic0d9af273a8a92177bf60e4be0dd5bddaf31868c
Reviewed-on: https://chromium-review.googlesource.com/c/1292058Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56853}

If the user's cleanup function didn't iterate all available WeakCells, we need
to schedule the cleanup task again at some point. The previous condition
resulted it never being scheduled.

BUG=v8:8179

Change-Id: I8f5f4c01d1eb6a3cca8bd21bdc52c38663889882
Reviewed-on: https://chromium-review.googlesource.com/c/1286686
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56772}

BUG=v8:8179

Change-Id: I29c5a5359a6e682ec6d94e9779f921889546b6a7
Reviewed-on: https://chromium-review.googlesource.com/c/1278393Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56711}

BUG=v8:8179

Change-Id: I528e64fafff2dc00808c48107799d39603f0ca48
Reviewed-on: https://chromium-review.googlesource.com/c/1275823
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56697}

These test mainly the data structures of JSWeakFactory / JSWeakCell.

BUG=v8:8179

Change-Id: I20ffd07c18bbb2e21c69d11aa65d1e245203cc82
Reviewed-on: https://chromium-review.googlesource.com/c/1267939
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56569}

Minimal implementation to run a simple example (see test) demonstrating the
weakness of WeakCell.

- Behind FLAG_harmony_weak_refs
- Add WeakFactory & WeakCell, no WeakRef in this version.

Spec clarifications: goo.gl/7ujBAk
Design doc: goo.gl/nvof2T

BUG=v8:8179

Change-Id: Iea2a7a2201e6380644235d190a542ab46e082382
Reviewed-on: https://chromium-review.googlesource.com/c/1238579Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56483}