Sets our main struct and passes it to the parent class.
Gets the child type.
Gets the child #GtkHeaderBar. Use hdy_header_group_child_get_child_type() to check the child type.
Gets the child #HdyHeaderBar. Use hdy_header_group_child_get_child_type() to check the child type.
Gets the child #HdyHeaderGroup. Use hdy_header_group_child_get_child_type() to check the child type.
Get the main Gtk struct
the main Gtk struct as a void*
the main Gtk struct