gdkwindow: Don't create a subsurface if we don't need to

In the case we have a native window, we don't need to crop it to a
non-native subrectangle, as abs_x / abs_y / width / height are all 0.

gdk/gdkwindow.c

@@ -3004,11 +3004,18 @@ _gdk_window_ref_cairo_surface (GdkWindow *window)
 
   surface = get_window_surface (window);
 
+  if (gdk_window_has_impl (window))
+    {
+      return surface;
+    }
+  else
+    {
       return cairo_surface_create_for_rectangle (surface,
                                                  window->abs_x,
                                                  window->abs_y,
                                                  window->width,
                                                  window->height);
+    }
 }
 
 /**