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

third_party/WebKit/LayoutTests/compositing/squashing/composited-bounds-for-negative-z-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true
     },
     {
       "name": "LayoutBlockFlow HTML",
       "bounds": [800, 408],
@@ skipping 31 matching lines @@
     {
       "name": "Overflow Controls Host Layer",
       "bounds": [300, 300]
     },
     {
       "name": "Vertical Scrollbar Layer",
       "position": [285, 0],
       "bounds": [15, 300]
     },
     {
+      "name": "Decoration Layer",
+      "bounds": [300, 300],
+      "drawsContent": true
+    },
+    {
       "name": "Squashing Containment Layer",
       "shouldFlattenTransform": false
     },
     {
       "name": "LayoutBlockFlow (relative positioned) DIV",
       "position": [108, 100],
       "bounds": [285, 1000]
     },
     {
       "name": "Squashing Layer (first squashed layer: LayoutBlockFlow (relative positioned) DIV)",
       "position": [108, 100],
       "bounds": [285, 1000],
       "drawsContent": true
     }
   ]
 }