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

Source/core/css/analyzer/DescendantInvalidationSet.cpp

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 58 matching lines @@
 void DescendantInvalidationSet::addId(const AtomicString& id)
 {
     m_ids.add(id);
 }
 
 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