Make all PaintLayers that scroll overflow self-painting.

third_party/WebKit/LayoutTests/platform/linux/paint/invalidation/textarea-caret-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
+          "object": "LayoutBlockFlow BODY",
+          "rect": [8, 8, 784, 43],
+          "reason": "geometry"
+        },
+        {
           "object": "LayoutTextControl TEXTAREA id='editor'",
           "rect": [7, 7, 183, 40],
           "reason": "subtree"
         },
         {
           "object": "LayoutText #text",
           "rect": [9, 11, 179, 16],
           "reason": "subtree"
         },
         {
           "object": "LayoutTextControl TEXTAREA id='editor'",
           "rect": [9, 30, 164, 15],
           "reason": "scroll control"
         },
         {
           "object": "LayoutTextControl TEXTAREA id='editor'",
           "rect": [173, 30, 15, 15],
           "reason": "scroll control"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
+      "object": "LayoutBlockFlow BODY",
+      "reason": "geometry"
+    },
+    {
+      "object": "RootInlineBox",
+      "reason": "geometry"
+    },
+    {
       "object": "LayoutTextControl TEXTAREA id='editor'",
       "reason": "subtree"
     },
     {
       "object": "LayoutTextControl TEXTAREA id='editor'",
       "reason": "geometry"
     },
     {
       "object": "HorizontalScrollbar",
       "reason": "scroll control"
@@ skipping 14 matching lines @@
       "object": "LayoutText #text",
       "reason": "subtree"
     },
     {
       "object": "InlineTextBox '------------------------------------------------------------'",
       "reason": "subtree"
     }
   ]
 }