update display metrics when switching to expanded desktop.. MUCH faster.

next phase is to change the logic for how the navbar is redrawn to make the statusbar
go to the bottom of the screen.

Change-Id: Ic2369e5227d67e9f84596660d96d1bfa9f92024f

Conflicts:
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java