[gtk/matthiasc/atspi-child] stack: Update HIDDEN a11y state for stack pages

[Matthias Clasen <matthiasc src gnome org>]

commit 9a943e21d382a21bdfe573ccd0f0e7dd4e3fc033
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Oct 24 22:04:26 2020 -0400

    stack: Update HIDDEN a11y state for stack pages
    
    This will let us handle additions and removals
    in the AT-SPI backend.

 gtk/gtkstack.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/gtk/gtkstack.c b/gtk/gtkstack.c
index b06bc3629d..fdf79fbe61 100644
--- a/gtk/gtkstack.c
+++ b/gtk/gtkstack.c
@@ -1304,6 +1304,10 @@ update_child_visible (GtkStack     *stack,
       gtk_widget_set_child_visible (priv->last_visible_child->widget, FALSE);
       priv->last_visible_child = NULL;
     }
+
+  gtk_accessible_update_state (GTK_ACCESSIBLE (child_info),
+                               GTK_ACCESSIBLE_STATE_HIDDEN, !visible,
+                               -1);
 }
 
 static void