Unfortunately the previous strategy was slower but more memory efficient. For now simply revert.

Revert "[zone] Use 32kb instead of 1MB as high zone page size"
Revert "[zone] Get rid of the Zone's segment pool"
Revert "[zone] Further simplify zone expansion, use single default page size"

Bug: chromium:908359
Change-Id: I649542e7e61eef0c14a26ffd21039e8340ab4d04
Reviewed-on: https://chromium-review.googlesource.com/c/1351027Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57872}