Make DecoratedCustomViewStyle notifications consistent.

Until now, we showed the collapsed state of DecoratedCustomViewStyle in two different ways depending on the target of the app.  In particular, we forced an awkward top line of views above the custom view for apps that didn't target S to ensure the context of the "subtext" was not lost from those notifications.  However, that context is available on expansion, and we think it's better if all apps get the same, more visually consistent behavior, regardless of the targeted SDK. 

Bug: 163626038
Change-Id: Ie50320566a97c8c05148857a6c4283a8870a833d
Test: manual