Multiple layout files with the same name now share a common interface.
They also share all variables no matter where it is defined.
If a variable is NOT used in one of the layout files, its implementation
does not create a field BUT STILL creates the setter (to implement
the base interface).
If the same view id is used for two different types of views, return
type in the interface is android.view.View. If it is an include,
the return value is IViewDataBinder.
Change-Id: Ie3cc2bb8ec5ea48b71337e314ec588a050d714df
