This reverts commit 45bbf804.

Reason for revert: Still some flakes.

Original change's description:
> Reland "Introducing an event loop mechanism for d8."
> 
> This reverts commit 02595c60.
> 
> Original CL: https://chromium-review.googlesource.com/c/494968/
> 
> Bug: 
> Change-Id: I7441ed91ebb4a087cdf437ae3239f9b021110a11
> Reviewed-on: https://chromium-review.googlesource.com/500947
> Reviewed-by: Bill Budge <bbudge@chromium.org>
> Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#45212}

TBR=bradnelson@chromium.org,bbudge@chromium.org,mtrofin@chromium.org,jochen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Bug: 
Change-Id: Idf2ea0431865104042a68bd2dac944a9725bf3f9
Reviewed-on: https://chromium-review.googlesource.com/501370Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45215}