Abstract away some of the complexity in CSSSelectorWatch by using HashCountedSet

Source/core/dom/CSSSelectorWatch.h

 /*
  * Copyright (C) 2013 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 16 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef CSSSelectorWatch_h
 #define CSSSelectorWatch_h
 
 #include "core/css/StyleRule.h"
 #include "core/dom/DocumentSupplementable.h"
 #include "platform/Timer.h"
+#include "wtf/HashCountedSet.h"
 #include "wtf/HashSet.h"
 #include "wtf/RefPtr.h"
 #include "wtf/Vector.h"
 #include "wtf/WeakPtr.h"
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
 class CSSSelectorWatch : public DocumentSupplement {
 public:
     virtual ~CSSSelectorWatch() { }
 
     static CSSSelectorWatch& from(Document&);
 
     void watchCSSSelectors(const Vector<String>& selectors);
     const Vector<RefPtr<StyleRule> >& watchedCallbackSelectors() const { return m_watchedCallbackSelectors; }
 
     void updateSelectorMatches(const Vector<String>& removedSelectors, const Vector<String>& addedSelectors);
 
 private:
     CSSSelectorWatch(Document&);
     void callbackSelectorChangeTimerFired(Timer<CSSSelectorWatch>*);
 
     Document& m_document;
 
     Vector<RefPtr<StyleRule> > m_watchedCallbackSelectors;
 
     // Maps a CSS selector string with a -webkit-callback property to the number
     // of matching RenderStyle objects in this document.
-    HashMap<String, int> m_matchingCallbackSelectors;
+    HashCountedSet<String> m_matchingCallbackSelectors;
     // Selectors are relative to m_matchingCallbackSelectors's contents at
     // the previous call to selectorMatchChanged.
     HashSet<String> m_addedSelectors;
     HashSet<String> m_removedSelectors;
 
     Timer<CSSSelectorWatch> m_callbackSelectorChangeTimer;
 
     // When an element is reparented, the new location's style is evaluated after the expriation of the relayout timer.
     // We don't want to send redundant callbacks to the embedder, so this counter lets us wait another time around the event loop.
     int m_timerExpirations;
 };
 
 } // namespace WebCore
 
 #endif // CSSSelectorWatch_h