[gtk/overlay-cleanup] Update migration guide for pass-through

[Matthias Clasen <matthiasc src gnome org>]

commit 4e97417efa315a0e708345d897924a15bb341840
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Feb 21 22:07:39 2019 -0500

    Update migration guide for pass-through

 docs/reference/gtk/migrating-3to4.xml | 9 +++++++++
 1 file changed, 9 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.xml b/docs/reference/gtk/migrating-3to4.xml
index 8b79b7bca1..0c453d4434 100644
--- a/docs/reference/gtk/migrating-3to4.xml
+++ b/docs/reference/gtk/migrating-3to4.xml
@@ -623,6 +623,15 @@
         GtkPasswordEntry.
       </para>
     </section>
+
+    <section>
+      <title>Adapt to changes in GtkOverlay API</title>
+      <para>
+        The GtkOverlay::pass-through child property has been replaced by the
+        GtkWidget::can-pick property. Note that they have the oppositve sense:
+        pass-through == !can-pick.
+      </para>
+    </section>
   </section>
 
 </chapter>