libgtk-3-0-dbg 3.18.8-1ubuntu2 (amd64 binary) in ubuntu xenial

 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 detached debugging symbols.
 .
 Most people will not need this package.