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

third_party/WebKit/LayoutTests/compositing/layer-creation/scroll-partial-update-expected.txt

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 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
@@ skipping 31 matching lines @@
       "drawsContent": true
     },
     {
       "name": "Overflow Controls Host Layer",
       "bounds": [200, 200]
     },
     {
       "name": "Vertical Scrollbar Layer",
       "position": [185, 0],
       "bounds": [15, 200]
+    },
+    {
+      "name": "Decoration Layer",
+      "bounds": [200, 200],
+      "drawsContent": true
     }
   ]
 }