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

third_party/WebKit/LayoutTests/paint/invalidation/overflow-hidden-yet-scrolled-with-custom-scrollbar-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
       "name": "LayoutBlockFlow DIV id='scroller'",
@@ skipping 17 matching lines @@
           "rect": [1, -399, 300, 600],
           "reason": "subtree"
         },
         {
           "object": "LayoutBlockFlow DIV id='target'",
           "rect": [1, 601, 100, 100],
           "reason": "subtree"
         },
         {
           "object": "LayoutBlockFlow DIV id='target'",
-          "rect": [1, 201, 100, 100],
-          "reason": "subtree"
-        },
-        {
-          "object": "LayoutBlockFlow DIV id='target'",
           "rect": [1, 689, 88, 12],
           "reason": "scroll"
         },
         {
           "object": "LayoutBlockFlow DIV id='target'",
           "rect": [1, 289, 88, 12],
           "reason": "scroll"
         },
         {
           "object": "LayoutBlockFlow DIV id='target'",
@@ skipping 43 matching lines @@
       "object": "VerticalScrollbar",
       "reason": "scroll"
     },
     {
       "object": "LayoutScrollbarPart (anonymous)",
       "reason": "scroll"
     }
   ]
 }