libgtk-3-0-udeb-dbgsym 3.18.9-1ubuntu3 (i386 binary) in ubuntu xenial

 This is a udeb, or a microdeb, for the debian-installer.
 .
 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 contains the minimal runtime library using X11 needed
 by the Debian installer.