This reverts commit 86da38fd.

Reason for revert: Linux64 TSAN bot failures

Original change's description:
> [heap] minor cleanup in allocation observer code
> 
> Change-Id: If0bec38d41a415e9fbfff57ac891de0461bac13b
> Reviewed-on: https://chromium-review.googlesource.com/668836
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Ali Ijaz Sheikh <ofrobots@google.com>
> Cr-Commit-Position: refs/heads/master@{#48046}

TBR=ulan@chromium.org,ofrobots@google.com

Change-Id: Idf03622c4e0f785c8a0d8e4015765a0849a99c47
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/668917Reviewed-by: Ali Ijaz Sheikh <ofrobots@google.com>
Commit-Queue: Ali Ijaz Sheikh <ofrobots@google.com>
Cr-Commit-Position: refs/heads/master@{#48051}