GtkScrolledWindow: Introduce a helper function
GtkScrolledWindow: Introduce a helper function

Instead of making assumptions about enum value ordering,
introduce a helper function to determine policy values
for which the scrollbar may be visible.

alexlarsson/gtk,chergert/gtk,chergert/gtk,chergert/gtk,davidgumberg/gtk,ahodesuka/gtk,jadahl/gtk,chergert/gtk,Adamovskiy/gtk,davidgumberg/gtk,Lyude/gtk-,jigpu/gtk,jigpu/gtk,ahodesuka/gtk,ahodesuka/gtk,ahodesuka/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jigpu/gtk,Adamovskiy/gtk,ahodesuka/gtk,davidgumberg/gtk,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,Lyude/gtk-,jadahl/gtk,Lyude/gtk-,Adamovskiy/gtk,jigpu/gtk,jadahl/gtk,alexlarsson/gtk,jadahl/gtk,davidgumberg/gtk,grubersjoe/adwaita,ahodesuka/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk,davidgumberg/gtk,Lyude/gtk-,Lyude/gtk-,jadahl/gtk,jigpu/gtk,grubersjoe/adwaita,alexlarsson/gtk,davidgumberg/gtk,chergert/gtk,alexlarsson/gtk,Adamovskiy/gtk,davidgumberg/gtk,chergert/gtk,Lyude/gtk-,jigpu/gtk,chergert/gtk,jigpu/gtk,davidgumberg/gtk,ahodesuka/gtk,chergert/gtk,jadahl/gtk,grubersjoe/adwaita,Adamovskiy/gtk,alexlarsson/gtk,ahodesuka/gtk,jadahl/gtk,Lyude/gtk-,Lyude/gtk-,Adamovskiy/gtk,jadahl/gtk