Moved visible region calculation to the server.

diff --git a/server/request.h b/server/request.h
index 84158ee..43dc9a9 100644
--- a/server/request.h
+++ b/server/request.h
@@ -251,6 +251,7 @@
 DECL_HANDLER(set_window_text);
 DECL_HANDLER(inc_window_paint_count);
 DECL_HANDLER(get_windows_offset);
+DECL_HANDLER(get_visible_region);
 DECL_HANDLER(set_window_property);
 DECL_HANDLER(remove_window_property);
 DECL_HANDLER(get_window_property);
@@ -430,6 +431,7 @@
     (req_handler)req_set_window_text,
     (req_handler)req_inc_window_paint_count,
     (req_handler)req_get_windows_offset,
+    (req_handler)req_get_visible_region,
     (req_handler)req_set_window_property,
     (req_handler)req_remove_window_property,
     (req_handler)req_get_window_property,