Implement style invalidation tree walk for targeted style recalc upon class change.

Source/core/css/analyzer/DescendantInvalidationSet.cpp

Index: Source/core/css/analyzer/DescendantInvalidationSet.cpp
diff --git a/Source/core/css/analyzer/DescendantInvalidationSet.cpp b/Source/core/css/analyzer/DescendantInvalidationSet.cpp
index 6249f197e84095c9c95f51e3d1ec75114840cdb6..e4c04af473f74096d6bffb7c3ef1cef5c53a874c 100644
--- a/Source/core/css/analyzer/DescendantInvalidationSet.cpp
+++ b/Source/core/css/analyzer/DescendantInvalidationSet.cpp
@@ -76,4 +76,10 @@ void DescendantInvalidationSet::addTagName(const AtomicString& tagName)
     m_tagNames.add(tagName);
 }
 
+void DescendantInvalidationSet::getClasses(Vector<AtomicString>& classes)
+{
+    for (HashSet<AtomicString>::const_iterator it = m_classes.begin(); it != m_classes.end(); ++it)
+        classes.append(*it);
+}
+
 } // namespace WebCore