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

third_party/WebKit/LayoutTests/compositing/overflow/content-gains-scrollbars-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
       "name": "LayoutBlockFlow (positioned) DIV class='container'",
@@ skipping 18 matching lines @@
     {
       "name": "Overflow Controls Host Layer",
       "bounds": [100, 100]
     },
     {
       "name": "Vertical Scrollbar Layer",
       "position": [85, 0],
       "bounds": [15, 100]
     },
     {
+      "name": "Decoration Layer",
+      "bounds": [100, 100],
+      "drawsContent": true
+    },
+    {
       "name": "LayoutBlockFlow (positioned) DIV class='container'",
       "position": [8, 13],
       "bounds": [100, 100],
       "shouldFlattenTransform": false,
       "drawsContent": true
     },
     {
       "name": "Scrolling Layer",
       "bounds": [100, 85],
       "shouldFlattenTransform": false
     },
     {
       "name": "Scrolling Contents Layer",
       "bounds": [200, 85]
     },
     {
       "name": "LayoutBlockFlow (positioned) DIV id='horizontal' class='content wide'",
       "bounds": [200, 10]
     },
     {
       "name": "Overflow Controls Host Layer",
       "bounds": [100, 100]
     },
     {
       "name": "Horizontal Scrollbar Layer",
       "position": [0, 85],
       "bounds": [100, 15]
     },
     {
+      "name": "Decoration Layer",
+      "bounds": [100, 100],
+      "drawsContent": true
+    },
+    {
       "name": "LayoutBlockFlow (positioned) DIV class='container'",
       "position": [8, 13],
       "bounds": [100, 100],
       "shouldFlattenTransform": false,
       "drawsContent": true
     },
     {
       "name": "Scrolling Layer",
       "bounds": [85, 85],
       "shouldFlattenTransform": false
@@ skipping 20 matching lines @@
       "position": [85, 0],
       "bounds": [15, 85]
     },
     {
       "name": "Scroll Corner Layer",
       "position": [85, 85],
       "bounds": [15, 15],
       "drawsContent": true
     },
     {
+      "name": "Decoration Layer",
+      "bounds": [100, 100],
+      "drawsContent": true
+    },
+    {
       "name": "LayoutBlockFlow (positioned) DIV id='corner' class='container resizeWidget'",
       "position": [8, 13],
       "bounds": [100, 100],
       "drawsContent": true
     },
     {
       "name": "Child Containment Layer",
       "bounds": [100, 100]
     },
     {
       "name": "LayoutBlockFlow (positioned) DIV class='content'",
       "bounds": [10, 10]
     },
     {
       "name": "Overflow Controls Host Layer",
       "bounds": [100, 100]
     },
     {
       "name": "Scroll Corner Layer",
       "position": [85, 85],
       "bounds": [15, 15],
       "drawsContent": true
     }
   ]
 }