Support invalidation sets for simple class selectors.

LayoutTests/fast/css/invalidation/targeted-class-style-invalidation.html

Index: LayoutTests/fast/css/invalidation/targeted-class-style-invalidation.html
diff --git a/LayoutTests/fast/css/invalidation/targeted-class-style-invalidation.html b/LayoutTests/fast/css/invalidation/targeted-class-style-invalidation.html
index cbf58d1b56417a4431fcd0a17f03bf5ec53d1eac..df733d145188eb14a9e3ec1ea41382ea602211af 100644
--- a/LayoutTests/fast/css/invalidation/targeted-class-style-invalidation.html
+++ b/LayoutTests/fast/css/invalidation/targeted-class-style-invalidation.html
@@ -4,6 +4,7 @@
 <style>
   div { width: 100px }
   .outer .inner { width: 200px }
+  .outer2 { width: 150px }
 </style>
 
 <div id="outer">
@@ -14,6 +15,9 @@
     <div id="inner2">
     </div>
 </div>
+<div id="outer2">
+    <div id="inner3"></div>
+</div>
 
 <script>
 description("Test that adding and removing class names only updates the elements that are affected.");
@@ -27,6 +31,7 @@ function insertStyleSheet(css)
 
 var outer = document.getElementById('outer');
 var inner = document.getElementById('inner');
+var outer2 = document.getElementById('outer2');
 
 var count;
 if (internals.runtimeFlags.targetedStyleRecalcEnabled)
@@ -51,4 +56,14 @@ inner.className = '';
 shouldBe("internals.updateStyleAndReturnAffectedElementCount()", '' + count);
 shouldBe("getComputedStyle(inner).width", '"100px"');
 
+if (internals.runtimeFlags.targetedStyleRecalcEnabled)
+    count = 1;
+else
+    count = 2;
+
+// Style recalc should happen on "outer2", but not "inner3".
+outer2.offsetTop;
+outer2.className = 'outer2';
+shouldBe("internals.updateStyleAndReturnAffectedElementCount()", '' + count);
+shouldBe("getComputedStyle(outer2).width", '"150px"');
 </script>