Fix the bug that negative outline-offset is covered up by composited

third_party/WebKit/LayoutTests/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
       "name": "LayoutBlockFlow DIV class='scroller'",
@@ skipping 24 matching lines @@
       "position": [305, 0],
       "bounds": [15, 325]
     },
     {
       "name": "Scroll Corner Layer",
       "position": [305, 325],
       "bounds": [15, 15],
       "drawsContent": true
     },
     {
+      "name": "Decoration Layer",
+      "bounds": [320, 340],
+      "drawsContent": true
+    },
+    {
       "name": "LayoutBlockFlow (relative positioned) DIV class='column'",
       "position": [10, 10],
       "bounds": [284, 1204],
       "contentsOpaque": true,
       "drawsContent": true,
       "backgroundColor": "#C0C0C0"
     }
   ]
 }