Don't invalidate rect if it's covered by fully invalidated parent's visual rect

third_party/WebKit/LayoutTests/paint/invalidation/resize-scrollable-iframe-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutBlockFlow (anonymous)",
           "rect": [8, 108, 784, 304],
           "reason": "forced by layout"
         },
         {
-          "object": "LayoutIFrame IFRAME id='iframe'",
-          "rect": [8, 108, 300, 300],
-          "reason": "forced by layout"
-        },
-        {
           "object": "LayoutView #document",
           "rect": [8, 193, 285, 200],
           "reason": "incremental"
         },
         {
           "object": "LayoutView #document",
           "rect": [8, 393, 285, 15],
           "reason": "scroll"
         },
         {
@@ skipping 58 matching lines @@
       "object": "VerticalScrollbar",
       "reason": "scroll"
     },
     {
       "object": "LayoutView #document",
       "reason": "incremental"
     }
   ]
 }