Howto retrieve selected font size from GtkFontButton

["Nelson Benítez León" <nbenitezl gmail com>]

Hi, 
Gtkfontbutton provides api to get the name of the selected font, but not to get the selected font size, so I would appreciate if you know of some way to get the size, or if that is not possible, if you will accept a patch to provide that api..

Thank you