Eagerly invalidate when a layer becomes stacking context

third_party/WebKit/LayoutTests/paint/invalidation/fixed-position-transparency-with-overflow-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 2016],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutBlockFlow (positioned) DIV class='absolute green'",
           "rect": [108, 308, 100, 100],
           "reason": "subtree"
         },
         {
+          "object": "LayoutBlockFlow (positioned) DIV class='absolute green'",
+          "rect": [108, 308, 100, 100],
+          "reason": "subtree"
+        },
+        {
           "object": "LayoutBlockFlow (relative positioned) DIV id='container' class='relative blue'",
           "rect": [8, 208, 100, 100],
           "reason": "subtree"
+        },
+        {
+          "object": "LayoutBlockFlow (relative positioned) DIV id='container' class='relative blue'",
+          "rect": [8, 208, 100, 100],
+          "reason": "subtree"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutBlockFlow (relative positioned) DIV id='container' class='relative blue'",
       "reason": "subtree"
     },
     {
       "object": "LayoutBlockFlow (positioned) DIV class='absolute green'",
       "reason": "subtree"
+    },
+    {
+      "object": "LayoutBlockFlow (relative positioned) DIV id='container' class='relative blue'",
+      "reason": "subtree"
+    },
+    {
+      "object": "LayoutBlockFlow (positioned) DIV class='absolute green'",
+      "reason": "subtree"
     }
   ]
 }