Add a vfunc to return a non-scrollable border around scrollables.
This would be nicer as a property, but we can't add properties
to an interface without breaking 3rd party implementations, so
make this an optional vfunc, and handle it not being set.
This patch adds the GtkScrollablePolicy type property to GtkScrollable
and implements it in all subclasses. GtkScrolledWindow observes this
property to make a good guess about when to show/hide scrollbars for
height-for-width content.
Most scrollable children do not do height-for-width *yet* but
most certainly will (toolpalette, treeview, iconview, textview
widgets all TODO), for scrollable widgets that do have a minimum
and natural size, it's important for them to observe the state
of this property in order to properly drive the scroll adjustments
according to the desired GtkScrollablePolicy. This patch makes
GtkViewport do this.
Patch also adds tests/testscrolledwindow.c to display the effects
of this property.
It is just too annoying to have to implement these properties in
every scrollable. Instead, we now have ::min-content-height/width
in GtkScrolledWindow.
We also add GtkScrollablePolicy to determine how to size the
scrollable content.
The GtkScrollable interface provides "hadjustment" and "vadjustment"
properties that are used by GtkScrolledWindow. It replaces
the ::set_scroll_adjustment signal. The scrollable interface
also has ::min-display-width/height properties that can be
used to control the minimally visible part inside a scrolled window.
