Doing some tests about PostAddToViewEvent, I notice this event is not called for UIViewRoot after the view is built.
The solution is do it manually on buildView() method after the view is populated.
There is another bug in 2.1.x branch related to markInitialState call. In
MYFACES-3367, it was used "javax.faces.IS_BUILDING_INITIAL_STATE" to detect if the view is build by first time, but in 2.1.x it is used to indicate if we call markInitialState or not. We need another different flag for that purpose, so I change it to "org.apache.myfaces.MARK_INITIAL_STATE" and fix "javax.faces.IS_BUILDING_INITIAL_STATE" to set and remove it like in 2.0.x branch.