Calculate paint invalidation rect for scrollbars

third_party/WebKit/LayoutTests/fast/repaint/window-resize-background-image-fixed-centered-composited-expected.txt

 {
   "bounds": [200, 300],
   "children": [
     {
       "bounds": [200, 300],
       "drawsContent": true,
       "repaintRects": [
         [0, 200, 200, 100],
         [0, 0, 200, 8]
       ],
       "paintInvalidationClients": [
-        "VerticalScrollbar",
         "LayoutView #document",
         "LayoutBlockFlow HTML"
       ]
     }
   ]
 }
 {
   "bounds": [300, 300],
   "children": [
     {
       "bounds": [300, 300],
       "drawsContent": true,
       "repaintRects": [
         [200, 0, 100, 300],
         [0, 0, 300, 300],
         [0, 0, 300, 8],
         [0, 0, 200, 8]
       ],
       "paintInvalidationClients": [
-        "HorizontalScrollbar",
         "LayoutView #document",
         "LayoutView #document",
         "LayoutBlockFlow HTML",
         "LayoutBlockFlow BODY"
       ]
     }
   ]
 }
 {
   "bounds": [300, 250],
@@ skipping 27 matching lines @@
       "paintInvalidationClients": [
         "LayoutView #document",
         "LayoutView #document",
         "LayoutBlockFlow HTML",
         "LayoutBlockFlow BODY"
       ]
     }
   ]
 }