Revert of [Athena, Cleanup] rename WidnowManager::GetInstance -> ::Get

Revert of [Athena, Cleanup] rename WidnowManager::GetInstance -> ::Get (patchset #1 id:40001 of https://codereview.chromium.org/599683003/)

Reason for revert:
http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%28dbg%29%283%29/builds/36880 AthenaEnvTest.TerminatingCallback  and DragHandleTest.ScrollTest started failing; this CL sounds related. Speculatively reverting.

Original issue's description:
> rename WidnowManager::GetInstance -> ::Get
> call OnTerminating in unit test.
> 
> BUG=None
> 
> Committed: https://crrev.com/828338e278350941febbfbede2b34d721be6dab1
> Cr-Commit-Position: refs/heads/master@{#296348}

TBR=mukai@chromium.org,skuhne@chromium.org,oshima@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=None

[Nico, 2014-09-24 15:34:59]

Created Revert of [Athena, Cleanup] rename WidnowManager::GetInstance -> ::Get

[commit-bot: I haz the power, 2014-09-24 15:35:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/599973002/1

[commit-bot: I haz the power, 2014-09-24 15:36:09]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-24 15:36:10]

Failed to apply the patch.