Revert 114095 - Move the concept of Activation to the Shell.

Revert 114095 - Move the concept of Activation to the Shell.

The Active Window is now stored in a property on the RootWindow. Classes wishing to observe changes to this can implement WindowObserver and attach to the RootWindow to be notified of changes in this property.

We provide an ActivationClient interface in Aura for customers to use to set/get the active window, and deactivate a window. This is because setting the active window involves more than just changing the property, there is some additional book-keeping that must be done. The ActivationClient is stored in a property on the RootWindow.

We also provide an ActivationDelegate interface in Aura that window owners can use to be notified of changes in activation state, and to specify whether or not a window can be activated. The ActivationDelegate should be stored on the relevant window in a property.

I moved a lot of Activation-related functionality out of Aura, including all of the unit tests, now on ActivationController, and the associated WindowDelegate implementations which have now become a single TestActivationDelegate implementation.

BUG=none
TEST=unit tests
Review URL: http://codereview.chromium.org/8894018

TBR=ben@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=114101