Revert of Only promote opaque scrollers which are stacking contexts.

third_party/WebKit/LayoutTests/paint/invalidation/flexbox/scrollbars-changed-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
+      "drawsContent": true
+    },
+    {
+      "name": "LayoutBlockFlow DIV id='scroller'",
+      "bounds": [200, 100],
+      "shouldFlattenTransform": false,
+      "drawsContent": true,
+      "backgroundColor": "#808080"
+    },
+    {
+      "name": "Scrolling Layer",
+      "bounds": [185, 100],
+      "shouldFlattenTransform": false
+    },
+    {
+      "name": "Scrolling Contents Layer",
+      "bounds": [185, 210],
+      "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutBlockFlow DIV id='dynamic' class='content'",
           "rect": [0, 0, 185, 30],
           "reason": "forced by layout"
         },
         {
-          "object": "LayoutBlockFlow DIV id='scroller'",
-          "rect": [185, 0, 15, 100],
-          "reason": "scroll"
-        },
-        {
           "object": "LayoutText #text",
           "rect": [0, 5, 15, 15],
           "reason": "full"
         }
       ]
+    },
+    {
+      "name": "Overflow Controls Host Layer",
+      "bounds": [200, 100]
+    },
+    {
+      "name": "Vertical Scrollbar Layer",
+      "position": [185, 0],
+      "bounds": [15, 100],
+      "paintInvalidations": [
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 210],
+          "reason": "full"
+        },
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 210],
+          "reason": "full"
+        },
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 210],
+          "reason": "full"
+        },
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 100],
+          "reason": "full"
+        },
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 100],
+          "reason": "full"
+        },
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 100],
+          "reason": "full"
+        },
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 100],
+          "reason": "full"
+        },
+        {
+          "object": "Vertical Scrollbar Layer",
+          "rect": [0, 0, 15, 100],
+          "reason": "full"
+        }
+      ]
     }
   ],
   "objectPaintInvalidations": [
     {
-      "object": "VerticalScrollbar",
-      "reason": "scroll"
-    },
-    {
       "object": "LayoutBlockFlow DIV id='dynamic' class='content'",
       "reason": "forced by layout"
     },
     {
       "object": "RootInlineBox",
       "reason": "forced by layout"
     },
     {
       "object": "LayoutText #text",
       "reason": "full"
     },
     {
       "object": "InlineTextBox 'z'",
       "reason": "full"
     }
   ]
 }