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

third_party/WebKit/LayoutTests/platform/linux/paint/invalidation/bugzilla-6473-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutBlockFlow DIV id='allcontent'",
           "rect": [8, 136, 784, 52],
           "reason": "style change"
         },
         {
           "object": "LayoutBlockFlow (relative positioned) P",
           "rect": [8, 152, 784, 20],
           "reason": "forced by layout"
         },
         {
-          "object": "LayoutBlockFlow (relative positioned) P",
-          "rect": [8, 136, 784, 20],
-          "reason": "forced by layout"
-        },
-        {
           "object": "LayoutText #text",
           "rect": [8, 152, 69, 19],
           "reason": "forced by layout"
-        },
-        {
-          "object": "LayoutText #text",
-          "rect": [8, 136, 69, 19],
-          "reason": "forced by layout"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutBlockFlow DIV id='allcontent'",
       "reason": "style change"
     },
     {
       "object": "LayoutBlockFlow (relative positioned) P",
       "reason": "forced by layout"
     },
     {
       "object": "RootInlineBox",
       "reason": "forced by layout"
     },
     {
       "object": "LayoutText #text",
       "reason": "forced by layout"
     },
     {
       "object": "InlineTextBox 'SUCCESS'",
       "reason": "forced by layout"
     }
   ]
 }