Move some scroll invalidations to the paint invalidation phase

LayoutTests/compositing/repaint/fixed-pos-inside-composited-intermediate-layer-expected.txt

 {
   "bounds": [785, 30020],
   "children": [
     {
       "bounds": [785, 30020],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "children": [
             {
               "position": [8, 8],
               "bounds": [500, 500],
               "contentsOpaque": true,
               "drawsContent": true,
               "backgroundColor": "#00FFFF"
             },
             {
               "position": [20, 20],
               "bounds": [100, 30000],
               "drawsContent": true,
               "repaintRects": [
-                [25, 25, 50, 150]
+                [25, 25, 50, 50]
               ]
             }
           ]
         }
       ]
     }
   ]
 }