Insulate SystemUI from IDs in inflated notification views.

We use the hidden View.setIsRootNamespace() in the same way
that AppWidgetHostView does: to block recursive ID search
traversals from traveling into notification views, which
might have children with IDs that collide with SystemUI's
own views. (Views inside notifications can still be located
by ID, but you need to start your search inside the
inflated notification row.)

Bug: 13421971
Change-Id: If8b81b9d0ed4b0eb6fa1e028275caa0b932f5759