Move window pings to MetaWindow

This will make it possible to use on Wayland as well...

src/core/window-private.h

@@ -466,6 +466,8 @@ struct _MetaWindow
 
   /* Bypass compositor hints */
   guint bypass_compositor;
+
+  GSList *pending_pings;
 };
 
 struct _MetaWindowClass
@@ -747,4 +749,16 @@ void meta_window_handle_enter (MetaWindow  *window,
 void meta_window_set_surface_mapped (MetaWindow *window,
                                      gboolean    surface_mapped);
 
+typedef void (* MetaWindowPingFunc) (MetaWindow  *window,
+				     guint32      timestamp,
+				     gpointer     user_data);
+
+void meta_window_ping (MetaWindow         *window,
+                       guint32             timestamp,
+                       MetaWindowPingFunc  ping_reply_func,
+                       MetaWindowPingFunc  ping_timeout_func,
+                       void               *user_data);
+void meta_window_pong (MetaWindow *window,
+                       guint32     timestamp);
+
 #endif