This reverts commit 6b810dad.

Reason for revert: Depends on another change that is causing gc-stress to fail.

Original change's description:
> [heap] Updated spaces Verify to check external memory count.
> 
> Bug: chromium:845409
> Change-Id: Ieb690f2d6ed699f306f1ff351cb5f62d9e2db860
> Reviewed-on: https://chromium-review.googlesource.com/1114820
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
> Cr-Commit-Position: refs/heads/master@{#54035}

TBR=ulan@chromium.org,hpayer@chromium.org,mlippautz@chromium.org,rfbpb@google.com

Change-Id: I72fcebf5485b991872e375d4b7c3e4aa6f70c41b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:845409
Reviewed-on: https://chromium-review.googlesource.com/1115480Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54042}