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

third_party/WebKit/LayoutTests/platform/mac/compositing/overflow/selection-gaps-after-removing-scrolling-contents-expected.txt

 This test passes if the container's scrolling contents layer (the first child of the GraphicsLayer with 4 children) draws content only on iterations 1 and 2, and its scrolling block selection layer (the child of the scrolling contents layer) draws content only on iteration 3. The scrolling block selection layer should also be much smaller than the scrolling contents layer.
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 Lorem Ipsum
 
 
 *** iteration 1: ***
 
 {
   "name": "Content Root Layer",
   "bounds": [800, 600],
   "children": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "name": "LayoutBlockFlow DIV id='container'",
           "position": [8, 80],
           "bounds": [300, 500],
-          "contentsOpaque": true,
           "shouldFlattenTransform": false,
           "drawsContent": true,
           "backgroundColor": "#0000FF",
           "children": [
             {
               "name": "Scrolling Layer",
               "bounds": [285, 485],
               "shouldFlattenTransform": false,
               "children": [
                 {
                   "name": "Scrolling Contents Layer",
                   "bounds": [285, 665],
+                  "contentsOpaque": true,
                   "drawsContent": true
                 }
               ]
             },
             {
               "name": "Overflow Controls Host Layer",
               "bounds": [300, 500],
               "children": [
                 {
                   "name": "Horizontal Scrollbar Layer",
@@ skipping 110 matching lines @@
     {
       "name": "LayoutView #document",
       "bounds": [785, 2751],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "name": "LayoutBlockFlow DIV id='container'",
           "position": [8, 80],
           "bounds": [300, 500],
-          "contentsOpaque": true,
           "shouldFlattenTransform": false,
           "drawsContent": true,
           "backgroundColor": "#0000FF",
           "children": [
             {
               "name": "Scrolling Layer",
               "bounds": [285, 485],
               "shouldFlattenTransform": false,
               "children": [
                 {
                   "name": "Scrolling Contents Layer",
                   "bounds": [285, 665],
+                  "contentsOpaque": true,
                   "drawsContent": true
                 }
               ]
             },
             {
               "name": "Overflow Controls Host Layer",
               "bounds": [300, 500],
               "children": [
                 {
                   "name": "Horizontal Scrollbar Layer",
@@ skipping 373 matching lines @@
           "bounds": [100, 50],
           "contentsOpaque": true,
           "drawsContent": true,
           "backgroundColor": "#FFA500"
         }
       ]
     }
   ]
 }