Revert of [Mac] Use a native MessagePump instead of a MessagePumpDefault

Revert of [Mac] Use a native MessagePump instead of a MessagePumpDefault (https://codereview.chromium.org/331513002/)

Reason for revert:
Broke Jingle unit tests on the bots.

Original issue's description:
> [Mac] Use a native MessagePump instead of a MessagePumpDefault
> 
> Many message loops in Chrome are backed by MessagePumpDefault which uses a WaitableEvent object to sleep, this is ultimately implemented as a pthread condition variable on POSIX.
> 
> In order to support timer coalescing in MessageLoops we need to sleep using a primitive which supports timer coalescing at the OS level (support for timer coalescing goes down into the kernel on Android/Linux/OSX/Win).  The current change achieves this and should provide a way to gauge the effect of timer coalescing.
> 
> An alternate approach to this patch would be to implement MessagePumpDefault using a primitive which supports timer coalescing.
> 
> Local performance tests didn't uncover any regressions from this change.
> 
> BUG=356804
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=276808

TBR=darin@chromium.org,mark@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=356804
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=276846

[jeremy, 2014-06-12 23:16:55]

Created Revert of [Mac] Use a native MessagePump instead of a MessagePumpDefault

[Mark Mentovai, 2014-06-12 23:19:00]

LGTM

[commit-bot: I haz the power, 2014-06-12 23:19:31]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jeremy@chromium.org/336603005/1

[commit-bot: I haz the power, 2014-06-12 23:22:50]

Change committed as 276846

[Lei Zhang, 2014-06-14 00:48:31]

base_unittests on Mac Valgrind wasn't happy either: http://goo.gl/wPBSgT

[jeremy, 2014-06-17 13:22:30]

thestig: Thanks! I've filed crbug.com/385604 to track when I reland the patch.