Do not cause unnecessary node lists invalidation on id/name attribute change

Source/core/html/HTMLCollection.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 23 matching lines @@
 
 class HTMLCollection : public ScriptWrappable, public RefCounted<HTMLCollection>, public LiveNodeListBase {
 public:
     enum ItemAfterOverrideType {
         OverridesItemAfter,
         DoesNotOverrideItemAfter,
     };
 
     static PassRefPtr<HTMLCollection> create(ContainerNode* base, CollectionType);
     virtual ~HTMLCollection();
-    virtual void invalidateCache() const OVERRIDE;
+    virtual void invalidateCache(Document* oldDocument = 0) const OVERRIDE;
 
     // DOM API
     unsigned length() const { return m_collectionIndexCache.nodeCount(*this); }
     Element* item(unsigned offset) const { return m_collectionIndexCache.nodeAt(*this, offset); }
     virtual Element* namedItem(const AtomicString& name) const;
     bool namedPropertyQuery(const AtomicString&, ExceptionState&);
     void namedPropertyEnumerator(Vector<String>& names, ExceptionState&);
 
     // Non-DOM API
     void namedItems(const AtomicString& name, Vector<RefPtr<Element> >&) const;
     bool isEmpty() const { return m_collectionIndexCache.isEmpty(*this); }
     bool hasExactlyOneItem() const { return m_collectionIndexCache.hasExactlyOneNode(*this); }
 
     // CollectionIndexCache API.
     bool canTraverseBackward() const { return !overridesItemAfter(); }
     Element* itemBefore(const Element* previousItem) const;
     Element* traverseToFirstElement(const ContainerNode& root) const;
     Element* traverseForwardToOffset(unsigned offset, Element& currentElement, unsigned& currentOffset, const ContainerNode& root) const;
 
 protected:
     HTMLCollection(ContainerNode* base, CollectionType, ItemAfterOverrideType);
 
     bool overridesItemAfter() const { return m_overridesItemAfter; }
     virtual Element* virtualItemAfter(Element*) const;
     bool shouldOnlyIncludeDirectChildren() const { return m_shouldOnlyIncludeDirectChildren; }
     virtual void supportedPropertyNames(Vector<String>& names);
 
-    virtual void updateNameCache() const;
-    bool hasNameCache() const { return m_isNameCacheValid; }
-    void setHasNameCache() const { m_isNameCacheValid = true; }
+    virtual void updateIdNameCache() const;
+    bool hasValidIdNameCache() const { return m_hasValidIdNameCache; }
+    void setHasValidIdNameCache() const
+    {
+        ASSERT(!m_hasValidIdNameCache);
+        m_hasValidIdNameCache = true;
+        document().incrementNodeListWithIdNameCacheCount();
+    }
 
     typedef HashMap<StringImpl*, OwnPtr<Vector<Element*> > > NodeCacheMap;
     Vector<Element*>* idCache(const AtomicString& name) const { return m_idCache.get(name.impl()); }
     Vector<Element*>* nameCache(const AtomicString& name) const { return m_nameCache.get(name.impl()); }
     void appendIdCache(const AtomicString& name, Element* element) const { append(m_idCache, name, element); }
     void appendNameCache(const AtomicString& name, Element* element) const { append(m_nameCache, name, element); }
 
 private:
     Element* traverseNextElement(Element& previous, const ContainerNode& root) const;
 
     static void append(NodeCacheMap&, const AtomicString&, Element*);
-    void invalidateIdNameCacheMaps() const
+    void invalidateIdNameCacheMaps(Document* oldDocument = 0) const
     {
+        if (!m_hasValidIdNameCache)
+            return;
+
+        // Make sure we decrement the NodeListWithIdNameCache count from
+        // the old document instead of the new one in the case the collection
+        // is moved to a new document.
+        unregisterIdNameCacheFromDocument(oldDocument ? *oldDocument : document());
+
         m_idCache.clear();
         m_nameCache.clear();
-        m_isNameCacheValid = false;
+        m_hasValidIdNameCache = false;
+    }
+
+    void unregisterIdNameCacheFromDocument(Document& document) const
+    {
+        ASSERT(m_hasValidIdNameCache);
+        document.decrementNodeListWithIdNameCacheCount();
     }
 
     const unsigned m_overridesItemAfter : 1;
     const unsigned m_shouldOnlyIncludeDirectChildren : 1;
-    mutable unsigned m_isNameCacheValid : 1;
+    mutable unsigned m_hasValidIdNameCache : 1;
     mutable NodeCacheMap m_idCache;
     mutable NodeCacheMap m_nameCache;
     mutable CollectionIndexCache<HTMLCollection, Element> m_collectionIndexCache;
 
     friend class LiveNodeListBase;
 };
 
 } // namespace
 
 #endif