Revert "Remove MessageLoopBase"

This reverts commit 58017e6cc6dd25207cae01ebe2d7961d12a46b3f.

Reason for revert: win-asan test failure

https://crbug.com/953465

Original change's description:
> Remove MessageLoopBase
> 
> Bug: 891670
> Change-Id: Iff6a2b4685f455509553779c7c04afd3c6f6c4e6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1538289
> Commit-Queue: Carlos Caballero <carlscab@google.com>
> Reviewed-by: Gabriel Charette <gab@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#651343}

TBR=gab@chromium.org,carlscab@google.com

Change-Id: I213af8c40d0b5db91abb6f84c9de531be3e18f98
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 891670
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1570660
Reviewed-by: Aleks Totic <atotic@chromium.org>
Commit-Queue: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#651461}
8 files changed