Move some scroll invalidations to the paint invalidation phase

LayoutTests/compositing/repaint/fixed-pos-with-composited-child-expected.txt

 {
   "bounds": [785, 4016],
   "children": [
     {
       "bounds": [785, 4016],
       "contentsOpaque": true,
       "drawsContent": true,
       "repaintRects": [
-        [0, 500, 400, 200]
+        [0, 600, 400, 100],
+        [0, 500, 400, 100]
       ],
       "children": [
         {
           "position": [0, 600],
           "bounds": [400, 100],
           "contentsOpaque": true,
           "backgroundColor": "#A0A0A0",
           "children": [
             {
               "bounds": [400, 100],
               "children": [
                 {
                   "bounds": [200, 100],
                   "contentsOpaque": true,
                   "drawsContent": true,
                   "backgroundColor": "#00A0A0"
                 }
               ]
             }
           ]
         }
       ]
     }
   ]
 }