Eagerly invalidate when a layer becomes stacking context

third_party/WebKit/LayoutTests/paint/invalidation/compositing/new-stacking-context-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
-      "name": "LayoutBlockFlow (positioned) DIV",
+      "name": "LayoutBlockFlow DIV",
       "position": [8, 8],
-      "contentsOpaque": true
+      "bounds": [100, 100],
+      "shouldFlattenTransform": false,
+      "drawsContent": true
     },
     {
-      "name": "Squashing Containment Layer",
+      "name": "Scrolling Layer",
+      "bounds": [100, 100],
       "shouldFlattenTransform": false
     },
     {
-      "name": "LayoutBlockFlow (relative positioned) DIV",
-      "position": [8, 8],
-      "bounds": [784, 52],
+      "name": "Scrolling Contents Layer",
+      "bounds": [200, 200],
       "drawsContent": true,
       "paintInvalidations": [
         {
-          "object": "LayoutBlockFlow DIV id='child'",
-          "rect": [1, 1, 100, 100],
-          "reason": "subtree"
-        },
-        {
           "object": "LayoutBlockFlow DIV id='target'",
-          "rect": [1, 1, 50, 50],
+          "rect": [0, 0, 200, 200],
           "reason": "subtree"
         }
       ]
     },
     {
-      "name": "Squashing Layer (first squashed layer: LayoutBlockFlow DIV id='target')",
-      "position": [9, 9],
-      "bounds": [100, 100],
+      "name": "Overflow Controls Host Layer",
+      "bounds": [100, 100]
+    },
+    {
+      "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": "LayoutBlockFlow DIV id='target'",
+      "position": [8, 8],
+      "bounds": [200, 200],
+      "opacity": 0.5,
+      "contentsOpaque": true,
       "drawsContent": true,
+      "backgroundColor": "#008000",
       "paintInvalidations": [
         {
-          "object": "LayoutBlockFlow DIV id='child'",
-          "rect": [0, 0, 100, 100],
-          "reason": "subtree"
+          "object": "LayoutBlockFlow DIV id='target'",
+          "rect": [0, 0, 200, 200],
+          "reason": "full"
         },
         {
           "object": "LayoutBlockFlow DIV id='target'",
-          "rect": [0, 0, 50, 50],
+          "rect": [0, 0, 200, 200],
           "reason": "subtree"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutBlockFlow DIV id='target'",
       "reason": "subtree"
     },
     {
-      "object": "LayoutBlockFlow DIV id='child'",
-      "reason": "subtree"
-    },
-    {
       "object": "LayoutBlockFlow DIV id='target'",
       "reason": "subtree"
     },
     {
-      "object": "LayoutBlockFlow DIV id='child'",
-      "reason": "subtree"
-    },
-    {
       "object": "LayoutBlockFlow DIV id='target'",
       "reason": "subtree"
-    },
-    {
-      "object": "LayoutBlockFlow DIV id='child'",
-      "reason": "subtree"
     }
   ]
 }