Fix gradient background invalidation when HTML size changes

third_party/WebKit/LayoutTests/platform/linux/paint/invalidation/compositing/iframe-inside-squashed-layer-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [785, 1016],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
       "name": "Squashing Containment Layer",
@@ skipping 12 matching lines @@
       "position": [8, 0],
       "bounds": [300, 654],
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutView #document",
           "rect": [0, 500, 300, 150],
           "reason": "style change"
         },
         {
-          "object": "LayoutBlockFlow HTML",
-          "rect": [0, 500, 300, 36],
-          "reason": "forced by layout"
-        },
-        {
-          "object": "LayoutBlockFlow HTML",
-          "rect": [0, 500, 285, 150],
-          "reason": "forced by layout"
-        },
-        {
           "object": "LayoutBlockFlow BODY",
           "rect": [8, 508, 284, 20],
           "reason": "forced by layout"
         },
         {
           "object": "LayoutBlockFlow BODY",
           "rect": [8, 508, 269, 142],
           "reason": "forced by layout"
         },
         {
@@ skipping 16 matching lines @@
     },
     {
       "object": "VerticalScrollbar",
       "reason": "scroll"
     },
     {
       "object": "LayoutView #document",
       "reason": "style change"
     },
     {
-      "object": "LayoutBlockFlow HTML",
-      "reason": "forced by layout"
-    },
-    {
       "object": "LayoutBlockFlow BODY",
       "reason": "forced by layout"
     },
     {
       "object": "RootInlineBox",
       "reason": "forced by layout"
     },
     {
       "object": "LayoutText #text",
       "reason": "forced by layout"
     },
     {
       "object": "InlineTextBox 'test1'",
       "reason": "forced by layout"
     }
   ]
 }