[metacity] tile-preview: avoid deprecated gtk_widget_is_composited

[Alberts Muktupāvels <muktupavels src gnome org>]

commit c4a9560184877770f67d560c6fede10d9c64725b
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Wed Nov 9 18:05:59 2016 +0200

    tile-preview: avoid deprecated gtk_widget_is_composited

 src/ui/tile-preview.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/ui/tile-preview.c b/src/ui/tile-preview.c
index 671b46f..484c1af 100644
--- a/src/ui/tile-preview.c
+++ b/src/ui/tile-preview.c
@@ -129,7 +129,7 @@ meta_tile_preview_composited_changed (GtkWidget *widget,
   GdkScreen *screen = gdk_screen_get_default ();
   GdkVisual *visual = gdk_screen_get_rgba_visual (screen);
 
-  preview->has_alpha = visual && gtk_widget_is_composited (widget);
+  preview->has_alpha = visual && gdk_screen_is_composited (screen);
 }
 
 MetaTilePreview *