This is a reland of 78f8ff95

Original change's description:
> [preparser] Refactor VariableProxies to use ThreadedLists interface
>
> Bug: v8:7926
> Change-Id: Idfc520b67696c8a838a0ee297ea392d416dd899e
> Reviewed-on: https://chromium-review.googlesource.com/1206292
> Commit-Queue: Florian Sattler <sattlerf@google.com>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55801}

Bug: v8:7926, chromium:883059
Change-Id: Icaa496be1b4df8306fe6d623e5825909d7b0c9c5
Reviewed-on: https://chromium-review.googlesource.com/1221529
Commit-Queue: Florian Sattler <sattlerf@google.com>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55833}