Use invalidation sets for nth invalidations.

third_party/WebKit/LayoutTests/fast/css/invalidation/nth-pseudo.html

Index: third_party/WebKit/LayoutTests/fast/css/invalidation/nth-pseudo.html
diff --git a/third_party/WebKit/LayoutTests/fast/css/invalidation/nth-pseudo.html b/third_party/WebKit/LayoutTests/fast/css/invalidation/nth-pseudo.html
index bcf504a1a783ba89ae960608d7158a09ac0db30c..9cffe1bc69afa870a8408646cf312fdf17a49e47 100644
--- a/third_party/WebKit/LayoutTests/fast/css/invalidation/nth-pseudo.html
+++ b/third_party/WebKit/LayoutTests/fast/css/invalidation/nth-pseudo.html
@@ -2,10 +2,13 @@
 <script src="../../../resources/testharness.js"></script>
 <script src="../../../resources/testharnessreport.js"></script>
 <style>
-    #t1 > :nth-child(even) {
+    #t1 > span:nth-child(even) {
         background-color: green
     }
-    #t2 > :nth-last-child(even) {
+    #t2 > span:nth-last-child(even) {
+        background-color: green
+    }
+    #t3 > .second:nth-child(2) {
         background-color: green
     }
 </style>
@@ -15,6 +18,12 @@
 <div id="t2">
     <span></span>
 </div>
+<div id="t3">
+    <div class="second"></div>
+    <div></div>
+    <div></div>
+    <div></div>
+</div>
 
 <script>
     function backgroundIsGreen(element) {
@@ -40,4 +49,13 @@
         assert_equals(internals.updateStyleAndReturnAffectedElementCount(), 1);
     }, "Prepending an element sibling should not affect :nth-last-child of succeeding siblings.");
 
+    test(() => {
+        t3.offsetTop;
+        let second = t3.querySelector(".second");
+        backgroundIsTransparent(second);
+        t3.insertBefore(document.createElement("div"), t3.firstChild);
+        assert_equals(internals.updateStyleAndReturnAffectedElementCount(), 2);
+        backgroundIsGreen(second);
+    }, "Prepending an element sibling should not affect :nth-last-child of succeeding siblings.");
+
 </script>