Fix gradient background invalidation when HTML size changes

third_party/WebKit/LayoutTests/paint/invalidation/fixed-and-absolute-position-scrolled-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 2016],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutView #document",
           "rect": [0, 2016, 800, 3792],
           "reason": "incremental"
         },
         {
-          "object": "LayoutBlockFlow HTML",
-          "rect": [0, 0, 800, 2016],
-          "reason": "forced by layout"
-        },
-        {
           "object": "LayoutBlockFlow (positioned) DIV id='absoluteDiv' class='absolute green'",
           "rect": [108, 5708, 100, 100],
           "reason": "subtree"
         },
         {
           "object": "LayoutBlockFlow (positioned) DIV id='absoluteDiv' class='absolute green'",
           "rect": [100, 700, 100, 100],
           "reason": "style change"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutBlockFlow (positioned) DIV id='absoluteDiv' class='absolute green'",
       "reason": "subtree"
     },
     {
       "object": "LayoutView #document",
       "reason": "incremental"
     },
     {
-      "object": "LayoutBlockFlow HTML",
-      "reason": "forced by layout"
-    },
-    {
       "object": "LayoutBlockFlow (positioned) DIV id='absoluteDiv' class='absolute green'",
       "reason": "style change"
     }
   ]
 }