Eagerly invalidate when a layer becomes stacking context

third_party/WebKit/LayoutTests/paint/invalidation/css-grid-layout/grid-item-z-index-change-repaint-expected.txt

Index: third_party/WebKit/LayoutTests/paint/invalidation/css-grid-layout/grid-item-z-index-change-repaint-expected.txt
diff --git a/third_party/WebKit/LayoutTests/paint/invalidation/css-grid-layout/grid-item-z-index-change-repaint-expected.txt b/third_party/WebKit/LayoutTests/paint/invalidation/css-grid-layout/grid-item-z-index-change-repaint-expected.txt
index df906021ec8ad46c6ded91720b6e96a3809b511b..3ebea7ec75ff9aa15b4f621b7a6eda0d7b7eeaf2 100644
--- a/third_party/WebKit/LayoutTests/paint/invalidation/css-grid-layout/grid-item-z-index-change-repaint-expected.txt
+++ b/third_party/WebKit/LayoutTests/paint/invalidation/css-grid-layout/grid-item-z-index-change-repaint-expected.txt
@@ -12,6 +12,11 @@
           "reason": "subtree"
         },
         {
+          "object": "LayoutBlockFlow DIV id='item2' class='sizedToGridArea green'",
+          "rect": [8, 236, 200, 100],
+          "reason": "subtree"
+        },
+        {
           "object": "LayoutBlockFlow DIV id='item1' class='sizedToGridArea green negativeZIndex'",
           "rect": [8, 126, 200, 100],
           "reason": "subtree"
@@ -21,6 +26,10 @@
   ],
   "objectPaintInvalidations": [
     {
+      "object": "LayoutBlockFlow DIV id='item2' class='sizedToGridArea green'",
+      "reason": "subtree"
+    },
+    {
       "object": "LayoutBlockFlow DIV id='item1' class='sizedToGridArea green negativeZIndex'",
       "reason": "subtree"
     },