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

third_party/WebKit/LayoutTests/platform/linux/paint/invalidation/caret-with-composited-scroll-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
       "name": "LayoutBlockFlow DIV id='scroller'",
@@ skipping 47 matching lines @@
       "name": "Horizontal Scrollbar Layer",
       "position": [0, 100],
       "bounds": [100, 0],
       "drawsContent": true
     },
     {
       "name": "Vertical Scrollbar Layer",
       "position": [100, 0],
       "bounds": [0, 100],
       "drawsContent": true
+    },
+    {
+      "name": "Decoration Layer",
+      "bounds": [100, 100],
+      "drawsContent": true
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "Caret",
       "reason": "invalidate paint rectangle"
     },
     {
       "object": "LayoutTextControl INPUT id='text'",
       "reason": "subtree"
     },
     {
       "object": "LayoutBlockFlow DIV id='inner-editor'",
       "reason": "subtree"
     },
     {
       "object": "Caret",
       "reason": "invalidate paint rectangle"
     },
     {
       "object": "Caret",
       "reason": "invalidate paint rectangle"
     }
   ]
 }