Comment 8 for bug 1649530

A grep on icontheme.h for lookup_icon returns this:

[lminiero@lminiero gtkmm] $ grep lookup_icon icontheme.h
 * Gtk::IconTheme::lookup_icon() includes builtin icons
 * Used to specify options for Gtk::IconTheme::lookup_icon()
  IconInfo lookup_icon(const Glib::ustring& icon_name, int size, IconLookupFlags flags) const;
  IconInfo lookup_icon(const Glib::ustring& icon_name, int size, int scale, IconLookupFlags flags) const;
  IconInfo lookup_icon(const Glib::RefPtr<const Gio::Icon>& icon, int size, IconLookupFlags flags) const;
  IconInfo lookup_icon(const Glib::RefPtr<const Gio::Icon>& icon, int size, int scale, IconLookupFlags flags) const;
   * lookup_icon() followed by Gtk::IconInfo::load_icon().
   * use lookup_icon() followed by
   * use lookup_icon() followed by