gtkScrolledWindowSetPlacement(object, window.placement)objectwindow.placementGTK_CORNER_TOP_LEFT, meaning the child is
in the top left, with the scrollbars underneath and to the right.
Other values in GtkCornerType are GTK_CORNER_TOP_RIGHT,
GTK_CORNER_BOTTOM_LEFT, and GTK_CORNER_BOTTOM_RIGHT.
See also gtkScrolledWindowGetPlacement and
gtkScrolledWindowUnsetPlacement.