Paint solid color backgrounds which are equivalent to locally attached into scrolling contents layer

third_party/WebKit/LayoutTests/virtual/prefer_compositing_to_lcd_text/compositing/overflow/scroll-parent-absolute-expected.txt

 {
   "name": "Content Root Layer",
   "bounds": [785, 5516],
   "children": [
     {
       "name": "LayoutView #document",
       "bounds": [785, 5516],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "name": "Squashing Containment Layer",
           "shouldFlattenTransform": false,
           "children": [
             {
               "name": "LayoutBlockFlow DIV id='top'",
               "position": [8, 8],
               "bounds": [500, 500],
-              "contentsOpaque": true,
               "shouldFlattenTransform": false,
               "drawsContent": true,
               "backgroundColor": "#0000FF",
               "children": [
                 {
                   "name": "Scrolling Layer",
                   "bounds": [485, 485],
                   "shouldFlattenTransform": false,
                   "children": [
                     {
                       "name": "Scrolling Contents Layer",
                       "bounds": [485, 5000],
+                      "contentsOpaque": true,
                       "drawsContent": true
                     }
                   ]
                 },
                 {
                   "name": "Overflow Controls Host Layer",
                   "bounds": [500, 500],
                   "children": [
                     {
                       "name": "Horizontal Scrollbar Layer",
@@ skipping 39 matching lines @@
           "contentsOpaque": true,
           "drawsContent": true,
           "backgroundColor": "#FA8072",
           "hasScrollParent": true
         }
       ]
     }
   ]
 }