[gtk/wip/matthiasc/popup5: 7/7] Mention gtk_widget_is_toplevel in the migration guide

[Matthias Clasen <matthiasc src gnome org>]

commit babab6a8e7c78d2ca2cdb4758c3185a7fd9a066a
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon May 20 03:54:59 2019 +0000

    Mention gtk_widget_is_toplevel in the migration guide

 docs/reference/gtk/migrating-3to4.xml | 8 ++++++++
 1 file changed, 8 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.xml b/docs/reference/gtk/migrating-3to4.xml
index 1db310271a..73f7a659b9 100644
--- a/docs/reference/gtk/migrating-3to4.xml
+++ b/docs/reference/gtk/migrating-3to4.xml
@@ -772,6 +772,14 @@
         gtk_widget_get_native() instead.
       </para>
     </section>
+
+    <section>
+      <title>gtk_widget_is_toplevel has been removed</title>
+      <para>
+        gtk_widget_is_toplevel() has been removed.
+        Use GTK_IS_ROOT, GTK_IS_NATIVE or GTK_IS_WINDOW
+        instead, as appropriate.
+      </para>
   </section>
 
 </chapter>