This relands commit ed3636e2..

Original change's description:
> [heap] Ensure that OOM callback is called before OOM.
>
> This patch also fixes MaxReserved() to accound for page headers and
> adds two tests for heap size and memory allocator size near OOM.
>
> Bug: chromium:824214
> Change-Id: I5bbe00a9d6a5798cdf4481861a10dca842244a63
> Reviewed-on: https://chromium-review.googlesource.com/973614
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52184}

TBR=machenbach@chromium.org


Change-Id: Idc3086a8b9dd30038f48cae64c9a8eb0b45ee372
Reviewed-on: https://chromium-review.googlesource.com/977913
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52200}