This is achieved by not having the decor view hold onto the activity
context. Instead, we are wrapping application context, so that we can
have theme support and also have a special instance of window manager
that is aware of the phone window (the same way as activity do).
This reverts commit a5ffea3b7d.
Change-Id: I924f4c7ef8f0d20e9174bd7b3e00ec00b44443b9