This is a reland of d4792e8f

Original change's description:
> [heap] Added per-page array buffer accouting (external memory).
> 
> Bug: chromium:845409
> Change-Id: Ibc568cdc501edf5d84d9c6379aff58be069369af
> Reviewed-on: https://chromium-review.googlesource.com/1114602
> Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#54028}

Bug: chromium:845409
Change-Id: I6b11d7f66313bcbcc31be9217c1b780cf3eaee99
Reviewed-on: https://chromium-review.googlesource.com/1116638
Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54066}