Revert of [Android] Mark posted UI thread tasks as asynchronous

Revert of [Android] Mark posted UI thread tasks as asynchronous (patchset #4 id:60001 of https://codereview.chromium.org/512333002/)

Reason for revert:
This patch was purely experimental, and the experiment has expired.

Original issue's description:
> [Android] Mark posted UI thread tasks as asynchronous
>
> Chromium shares a message loop with Android on the browser UI thread.
> This can cause problems when the associated Looper has a sync barrier,
> preventing posted Chromium tasks from being dispatched until the
> barrier is removed. Make this sharing more fair by marking all Chromium
> Message tasks as asynchronous, avoiding stalls when there is a sync
> barrier.
>
> Note: This change is for gathering data about the perf impact and we'll
> revert it before cutting a release branch.
>
> BUG=407149, 380781, 407133
>
> Committed: https://crrev.com/feabeebb3ac5810f896ac8303a77ee695acaf9d4
> Cr-Commit-Position: refs/heads/master@{#292551}

TBR=aelias@chromium.org,epenner@chromium.org,nyquist@chromium.org,sievers@chromium.org,skyostil@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=407149, 380781, 407133
Committed: https://crrev.com/1dcbab8b36837b7c43bf18f778d0363fa0af9b8a
Cr-Commit-Position: refs/heads/master@{#294875}

[jdduke (slow), 2014-09-15 18:28:32]

Created Revert of [Android] Mark posted UI thread tasks as asynchronous

[aelias_OOO_until_Jul13, 2014-09-15 18:33:55]

lgtm

[commit-bot: I haz the power, 2014-09-15 19:16:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/564373005/1

[nyquist, 2014-09-15 19:57:33]

rs lgtm

[commit-bot: I haz the power, 2014-09-15 20:05:07]

Committed patchset #1 (id:1) as 2a519e70b3f35fb7f3a944d7a5e92bb96e3e3ab8

[commit-bot: I haz the power, 2014-09-15 20:06:27]

Patchset 1 (id:??) landed as
https://crrev.com/1dcbab8b36837b7c43bf18f778d0363fa0af9b8a
Cr-Commit-Position: refs/heads/master@{#294875}