MetaWindowActor: don't draw shadows for tiled windows with a match

The shadow between 2 tiled windows ruins the visual tiles effect.

https://bugzilla.gnome.org/show_bug.cgi?id=643075

src/compositor/meta-window-actor.c

@@ -739,6 +739,13 @@ meta_window_actor_has_shadow (MetaWindowActor *self)
       meta_window_is_fullscreen (priv->window))
     return FALSE;
 
+  /*
+   * If we have two snap-tiled windows, we don't want the shadow to obstruct
+   * the other window.
+   */
+  if (meta_window_get_tile_match (priv->window))
+    return FALSE;
+
   /*
    * Always put a shadow around windows with a frame - This should override
    * the restriction about not putting a shadow around ARGB windows.