gir1.2-gtk-3.0 3.12.2-0ubuntu15.2 (amd64 binary) in ubuntu utopic

 GTK+ is a multi-platform toolkit for creating graphical user
 interfaces. Offering a complete set of widgets, GTK+ is suitable
 for projects ranging from small one-off tools to complete application
 suites.
 .
 This package can be used by other packages using the GIRepository format to
 generate dynamic bindings.