wayland: Add internal API for handling Wayland serial numbers

We need to keep track of the serial numbers for various API requests.

gdk/wayland/gdkdisplay-wayland.c

@@ -637,3 +637,17 @@ _gdk_wayland_display_load_cursor_theme (GdkWaylandDisplay *wayland_display)
                                                         w,
                                                         wayland_display->shm);
 }
+
+guint32
+_gdk_wayland_display_get_serial (GdkWaylandDisplay *wayland_display)
+{
+  return wayland_display->serial;
+}
+
+void
+_gdk_wayland_display_update_serial (GdkWaylandDisplay *wayland_display,
+                                    guint32            serial)
+{
+  if (serial > wayland_display->serial)
+    wayland_display->serial = serial;
+}

gdk/wayland/gdkdisplay-wayland.h

@@ -70,8 +70,9 @@ struct _GdkWaylandDisplay
   /* Startup notification */
   gchar *startup_notification_id;
 
-  /* Time of most recent user interaction. */
+  /* Time of most recent user interaction and most recent serial */
   gulong user_time;
+  guint32 serial;
 
   /* Wayland fields below */
   struct wl_display *wl_display;

gdk/wayland/gdkprivate-wayland.h

@@ -155,4 +155,7 @@ void _gdk_wayland_window_set_device_grabbed (GdkWindow      *window,
                                              struct wl_seat *seat,
                                              guint32         time_);
 
+guint32 _gdk_wayland_display_get_serial (GdkWaylandDisplay *wayland_display);
+void _gdk_wayland_display_update_serial (GdkWaylandDisplay *wayland_display, guint32 serial);
+
 #endif /* __GDK_PRIVATE_WAYLAND_H__ */