Revert 175648 because it causes http://crbug.com/169126.

Revert 175648 because it causes http://crbug.com/169126.

> Connect to DesktopEnvironment's stubs only when audio/video schedulers are about to be created.
> 
> This CL localizes usage of DesktopEnvironment to a single method that creates audio/video schedulers and hook up the event executor. This prepares further refactoring of DesktopEnvironment that should become a factory for classes interacting with the specific desktop environment.
> 
> Related changes in this CL:
>   - MouseClampingFilter receives screen size on the proper thread.
>   - ClientSessionTest.* tests now run asynchronously to support MouseClampingFilter change.
>   - ClientSession does not expose DesktopEnvironment.
>   - InputEventTracker can be re-attached to a different InputStub.
> 
> BUG=104544
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/11781003

TBR=alexeypa@chromium.org
BUG=104544, 169126
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=176126