freeze break in gtk

[Matthias Clasen <matthias clasen gmail com>]

I'm going to merge the patch from

https://bugzilla.gnome.org/show_bug.cgi?id=757943

It undoes a behavior change in scrolledwindow sizing that happend
during the last cycle, and broke the expected outcome in many
situations (e.g. scrolling content in popovers). We'll add new api to
opt-in to the new behavior
instead.