Fix visual rect for background box painting in composited scrollers.

third_party/WebKit/LayoutTests/fast/repaint/overflow-scroll-local-background-text-color-change-expected.txt

 {
   "name": "Content Root Layer",
   "bounds": [800, 600],
   "children": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "name": "LayoutBlockFlow DIV id='scroller'",
           "position": [8, 8],
           "bounds": [200, 200],
           "shouldFlattenTransform": false,
           "drawsContent": true,
-          "backgroundColor": "#008000",
+          "backgroundColor": "#0000FF",
           "paintInvalidations": [
             {
               "object": "LayoutBlockFlow DIV id='scroller'",
               "rect": [0, 0, 200, 200],
               "reason": "style change"
             }
           ],
           "children": [
             {
               "name": "Scrolling Layer",
               "bounds": [185, 185],
               "shouldFlattenTransform": false,
               "children": [
                 {
                   "name": "Scrolling Contents Layer",
-                  "bounds": [185, 300],
+                  "bounds": [185, 552],
                   "contentsOpaque": true,
                   "drawsContent": true,
                   "paintInvalidations": [
                     {
                       "object": "LayoutBlockFlow DIV id='scroller'",
-                      "rect": [0, 0, 185, 300],
+                      "rect": [0, 0, 185, 552],
                       "reason": "style change"
                     }
                   ]
                 }
               ]
             },
             {
               "name": "Overflow Controls Host Layer",
               "bounds": [200, 200],
               "children": [
                 {
                   "name": "Horizontal Scrollbar Layer",
                   "position": [0, 185],
-                  "bounds": [185, 15]
+                  "bounds": [185, 15],
+                  "paintInvalidations": [
+                    {
+                      "object": "Horizontal Scrollbar Layer",
+                      "rect": [0, 0, 185, 15],
+                      "reason": "full"
+                    }
+                  ]
                 },
                 {
                   "name": "Vertical Scrollbar Layer",
                   "position": [185, 0],
-                  "bounds": [15, 185]
+                  "bounds": [15, 185],
+                  "paintInvalidations": [
+                    {
+                      "object": "Vertical Scrollbar Layer",
+                      "rect": [0, 0, 15, 185],
+                      "reason": "full"
+                    },
+                    {
+                      "object": "Vertical Scrollbar Layer",
+                      "rect": [0, 0, 15, 185],
+                      "reason": "full"
+                    }
+                  ]
                 },
                 {
                   "name": "Scroll Corner Layer",
                   "position": [185, 185],
                   "bounds": [15, 15],
                   "drawsContent": true
                 }
               ]
             }
           ]
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
+      "object": "Scrolling Contents Layer",
+      "reason": "style change"
+    },
+    {
       "object": "LayoutBlockFlow DIV id='scroller'",
       "reason": "style change"
     }
   ]
 }