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

Source/core/css/analyzer/DescendantInvalidationSet.h

 /*
  * 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 39 matching lines @@
     {
         return adoptRef(new DescendantInvalidationSet);
     }
 
     void combine(const DescendantInvalidationSet& other);
 
     void addClass(const AtomicString& className);
     void addId(const AtomicString& id);
     void addTagName(const AtomicString& tagName);
 
+    // Appends the classes in this DescendantInvalidationSet to the vector.
+    void getClasses(Vector<AtomicString>& classes);
+
     void setWholeSubtreeInvalid() { m_allDescendantsMightBeInvalid = true; };
-
+    bool wholeSubtreeInvalid() { return m_allDescendantsMightBeInvalid; }
 private:
     DescendantInvalidationSet();
 
     bool invalidateElementSubtreeInternal(Element*);
     // If true, all descendants might be invalidated, so a full subtree recalc is required.
     bool m_allDescendantsMightBeInvalid;
 
     // FIXME: optimize this if it becomes a memory issue.
     HashSet<AtomicString> m_classes;
     HashSet<AtomicString> m_ids;
     HashSet<AtomicString> m_tagNames;
 };
 
 } // namespace WebCore
 
 #endif // DescendantInvalidationSet_h