xwayland: Split up xwl_screen_post_damage into two phases

The first phase sets the new surface properties for all damaged
windows, then the second phase commits all surface updates.

This is preparatory for the next change, there should be no observable
change in behaviour (other than the order of Wayland protocol
requests).
Reviewed-by: Adam Jackson <ajax@redhat.com>

hw/xwayland/xwayland-screen.c

@@ -273,6 +273,9 @@ static void
 xwl_screen_post_damage(struct xwl_screen *xwl_screen)
 {
     struct xwl_window *xwl_window, *next_xwl_window;
+    struct xorg_list commit_window_list;
+
+    xorg_list_init(&commit_window_list);
 
     xorg_list_for_each_entry_safe(xwl_window, next_xwl_window,
                                   &xwl_screen->damage_window_list, link_damage) {
@@ -290,6 +293,17 @@ xwl_screen_post_damage(struct xwl_screen *xwl_screen)
 #endif
 
         xwl_window_post_damage(xwl_window);
+        xorg_list_del(&xwl_window->link_damage);
+        xorg_list_append(&xwl_window->link_damage, &commit_window_list);
+    }
+
+    if (xorg_list_is_empty(&commit_window_list))
+        return;
+
+    xorg_list_for_each_entry_safe(xwl_window, next_xwl_window,
+                                  &commit_window_list, link_damage) {
+        wl_surface_commit(xwl_window->surface);
+        xorg_list_del(&xwl_window->link_damage);
     }
 }
 

hw/xwayland/xwayland-window.c

@@ -808,10 +808,7 @@ xwl_window_post_damage(struct xwl_window *xwl_window)
     }
 
     xwl_window_create_frame_callback(xwl_window);
-    wl_surface_commit(xwl_window->surface);
     DamageEmpty(window_get_damage(xwl_window->window));
-
-    xorg_list_del(&xwl_window->link_damage);
 }
 
 Bool