Revert of Revert of Forward input and compositing tasks to the Blink scheduler

Revert of Revert of Forward input and compositing tasks to the Blink scheduler (patchset #1 id:1 of https://codereview.chromium.org/548253002/)

Reason for revert:
this didn't reduce flakiness

Original issue's description:
> Revert of Forward input and compositing tasks to the Blink scheduler (patchset #21 id:400001 of https://codereview.chromium.org/363383002/)
> 
> Reason for revert:
> suspecting it's causing the high rate of flakes in Instrumentation test ContentShellTest
> 
> BUG=411756
> 
> Original issue's description:
> > Forward input and compositing tasks to the Blink scheduler
> > 
> > Instead of posting input and compositor tasks directly to the 
> > main thread message loop, forward them to the Blink scheduler 
> > so they can be prioritized over other tasks.
> > 
> > BUG=391005
> > 
> > Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=290845
> > 
> > Committed: https://chromium.googlesource.com/chromium/src/+/68bab3290b45a8610ad875d3c92530477c16a948
> 
> TBR=jamesr@chromium.org,alexclarke@chromium.org,picksi@chromium.org,eseidel@chromium.org,skyostil@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=391005
> 
> Committed: https://chromium.googlesource.com/chromium/src/+/66f85d5405417e6ddd11e1b9be677062a2e3ae4f

TBR=jamesr@chromium.org,alexclarke@chromium.org,picksi@chromium.org,eseidel@chromium.org,skyostil@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=411756
Committed: https://crrev.com/479004ba3d84ec815444e9279adcda7ed056afcb
Cr-Commit-Position: refs/heads/master@{#293722}

[jam, 2014-09-08 14:36:48]

Created Revert of Revert of Forward input and compositing tasks to the Blink
scheduler

[commit-bot: I haz the power, 2014-09-08 14:38:20]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jam@chromium.org/548333002/1

[commit-bot: I haz the power, 2014-09-08 14:41:44]

Committed patchset #1 (id:1) as 84f27546bec0deecdf15e28ab1fd85a40e7226f4

[commit-bot: I haz the power, 2014-09-10 03:46:12]

Patchset 1 (id:??) landed as
https://crrev.com/479004ba3d84ec815444e9279adcda7ed056afcb
Cr-Commit-Position: refs/heads/master@{#293722}