Fix flattening for scrollable areas.

third_party/WebKit/LayoutTests/platform/linux/virtual/prefer_compositing_to_lcd_text/compositing/overflow/updating-scrolling-container-and-content-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "position": [8, 108],
           "bounds": [200, 200],
+          "shouldFlattenTransform": false,
           "drawsContent": true,
           "repaintRects": [
             [0, 190, 74, 19],
             [0, 170, 74, 19],
             [0, 150, 74, 19],
             [0, 130, 74, 19],
             [0, 110, 74, 19],
             [0, 90, 74, 19],
             [0, 70, 74, 19],
             [0, 50, 74, 19],
             [0, 30, 74, 19],
             [0, 10, 74, 19],
             [0, -10, 74, 19],
             [0, -30, 74, 19],
             [0, -50, 74, 19]
           ],
           "children": [
             {
               "bounds": [185, 185],
+              "shouldFlattenTransform": false,
               "children": [
                 {
                   "bounds": [185, 260],
-                  "shouldFlattenTransform": false,
                   "drawsContent": true,
                   "repaintRects": [
                     [0, 240, 74, 19],
                     [0, 220, 74, 19],
                     [0, 200, 74, 19],
                     [0, 180, 74, 19],
                     [0, 160, 74, 19],
                     [0, 140, 74, 19],
                     [0, 120, 74, 19],
                     [0, 100, 74, 19],
@@ skipping 52 matching lines @@
                 }
               ]
             }
           ]
         }
       ]
     }
   ]
 }