Hah, I've spent all of yesterday trying to figure this out but as soon I've posted my question I've found the answer myself.
I was trying to repaint the dialog after setting overflow: auto
manually by calling win._bindings.repaint[0]()
and it gave me an error:
Cannot read property 'autoScroll' of undefined
And it turned out that autoScroll
is what I was looking for:
editor.windowManager.open({
autoScroll: true,
height: 300,
...
});