gdk/surface: Make backends aware of when layout is requested

gdk/gdksurface.c

@@ -1378,8 +1378,13 @@ gdk_surface_layout_on_clock (GdkFrameClock *clock,
 void
 gdk_surface_request_layout (GdkSurface *surface)
 {
+  GdkSurfaceClass *class;
   GdkFrameClock *frame_clock;
 
+  class = GDK_SURFACE_GET_CLASS (surface);
+  if (class->request_layout)
+    class->request_layout (surface);
+
   if (surface->update_freeze_count ||
       gdk_surface_is_toplevel_frozen (surface))
     {

gdk/gdksurfaceprivate.h

@@ -170,6 +170,7 @@ struct _GdkSurfaceClass
                                            gboolean        attached,
                                            GdkGLContext   *share,
                                            GError        **error);
+  void         (* request_layout)         (GdkSurface     *surface);
   void         (* compute_size)           (GdkSurface     *surface);
 };