Move paint invalidation after compositing update

LayoutTests/fast/css-grid-layout/grid-item-z-index-change-repaint-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "repaintRects": [
         [8, 236, 200, 100],
         [8, 236, 200, 100],
+        [8, 236, 200, 100],
         [8, 126, 200, 100],
         [8, 126, 200, 100]
       ]
     }
   ]
 }