[libwnck] test-tasklist: avoid deprecated gtk_widget_is_composited

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 0b90c90a1feba651a1d2bff5a63793b0d461bd04
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sat Nov 12 00:46:18 2016 +0200

    test-tasklist: avoid deprecated gtk_widget_is_composited

 libwnck/test-tasklist.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/libwnck/test-tasklist.c b/libwnck/test-tasklist.c
index 5f94ee2..0912cc8 100644
--- a/libwnck/test-tasklist.c
+++ b/libwnck/test-tasklist.c
@@ -40,9 +40,11 @@ static void
 window_composited_changed (GtkWidget *widget,
                            gpointer   user_data)
 {
+  GdkScreen *screen;
   gboolean composited;
 
-  composited = gtk_widget_is_composited (widget);
+  screen = gdk_screen_get_default ();
+  composited = gdk_screen_is_composited (screen);
 
   gtk_widget_set_app_paintable (widget, composited);
 }