Include scroll offset in scrolling contents painted background rect invalidation.

third_party/WebKit/LayoutTests/paint/invalidation/composited-overflow-with-local-background-expected.txt

 {
   "name": "Content Root Layer",
   "bounds": [800, 600],
   "children": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
@@ skipping 18 matching lines @@
               "shouldFlattenTransform": false,
               "children": [
                 {
                   "name": "Scrolling Contents Layer",
                   "bounds": [185, 300],
                   "contentsOpaque": true,
                   "drawsContent": true,
                   "paintInvalidations": [
                     {
                       "object": "LayoutBlockFlow DIV id='scroller'",
-                      "rect": [0, 0, 185, 300],
+                      "rect": [0, -100, 185, 300],
                       "reason": "style change"
                     }
                   ]
                 }
               ]
             },
             {
               "name": "Overflow Controls Host Layer",
               "bounds": [200, 200],
               "children": [
@@ skipping 25 matching lines @@
       "object": "Scrolling Contents Layer",
       "reason": "style change"
     },
     {
       "object": "LayoutBlockFlow DIV id='scroller'",
       "reason": "style change"
     }
   ]
 }