Fix gradient background invalidation when HTML size changes

third_party/WebKit/LayoutTests/platform/linux/paint/invalidation/text-match-document-change-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
-          "object": "LayoutBlockFlow HTML",
-          "rect": [10, 102, 285, 400],
-          "reason": "forced by layout"
-        },
-        {
           "object": "LayoutBlockFlow DIV id='to-be-changed'",
           "rect": [18, 130, 269, 40],
           "reason": "full"
         },
         {
           "object": "LayoutText #text",
           "rect": [18, 130, 235, 39],
           "reason": "layoutObject removal"
         },
         {
@@ skipping 12 matching lines @@
   "objectPaintInvalidations": [
     {
       "object": "LayoutText #text",
       "reason": "layoutObject removal"
     },
     {
       "object": "VerticalScrollbar",
       "reason": "scroll"
     },
     {
-      "object": "LayoutBlockFlow HTML",
-      "reason": "forced by layout"
-    },
-    {
       "object": "LayoutBlockFlow DIV id='to-be-changed'",
       "reason": "full"
     },
     {
       "object": "RootInlineBox",
       "reason": "full"
     },
     {
       "object": "LayoutText #text",
       "reason": "layoutObject insertion"
     },
     {
       "object": "InlineTextBox 'After change'",
       "reason": "layoutObject insertion"
     }
   ]
 }