Add shell_util_get_transformed_allocation()

Add a function that gets the current allocation of an actor
transformed into stage coordinates. This avoids a misfeature of
clutter_actor_get_transformed_size() where when a size request is
queued (even if it won't eventually change the size), the returned
value is the transformed size request rather than the last allocation.

https://bugzilla.gnome.org/show_bug.cgi?id=645744

src/shell-util.h

@@ -13,6 +13,9 @@ GIcon *shell_util_get_icon_for_uri (const char *text_uri);
 GIcon *shell_util_icon_from_string (const char *string, GError **error);
 void   shell_util_set_hidden_from_pick (ClutterActor *actor, gboolean hidden);
 
+void shell_util_get_transformed_allocation (ClutterActor    *actor,
+                                            ClutterActorBox *box);
+
 char *shell_util_format_date (const char *format,
                               gint64      time_ms);