This is a reland of f3c8da56
Original change's description:
> [heap] Use weak cell in normalized map cache.
> 
> This replaces ad-hoc weakness in normalized map cache with weak cell.
> 
> Bug: chromium:694255
> Change-Id: I6a12301b2176fe3723b56178a65582cfb412f7d2
> Reviewed-on: https://chromium-review.googlesource.com/704834
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48344}

Bug: chromium:694255
Change-Id: I181a9c02cc934373e40455f1be02f1caf140639b
Reviewed-on: https://chromium-review.googlesource.com/709354Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48442}