Make TreeScope::documentScope() return a reference and ensure m_documentScope is never NULL

Source/core/dom/NodeRareData.h

 /*
  * Copyright (C) 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 David Smith <catfish.man@gmail.com>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 158 matching lines @@
     bool isEmpty() const
     {
         return m_atomicNameCaches.isEmpty() && m_nameCaches.isEmpty() && m_tagNodeListCacheNS.isEmpty();
     }
 
     void adoptTreeScope()
     {
         invalidateCaches();
     }
 
-    void adoptDocument(Document* oldDocument, Document* newDocument)
+    void adoptDocument(Document& oldDocument, Document& newDocument)
     {
         invalidateCaches();
 
         if (oldDocument != newDocument) {
             NodeListAtomicNameCacheMap::const_iterator atomicNameCacheEnd = m_atomicNameCaches.end();
             for (NodeListAtomicNameCacheMap::const_iterator it = m_atomicNameCaches.begin(); it != atomicNameCacheEnd; ++it) {
                 LiveNodeListBase* list = it->value;
-                oldDocument->unregisterNodeList(list);
-                newDocument->registerNodeList(list);
+                oldDocument.unregisterNodeList(list);
+                newDocument.registerNodeList(list);
             }
 
             NodeListNameCacheMap::const_iterator nameCacheEnd = m_nameCaches.end();
             for (NodeListNameCacheMap::const_iterator it = m_nameCaches.begin(); it != nameCacheEnd; ++it) {
                 LiveNodeListBase* list = it->value;
-                oldDocument->unregisterNodeList(list);
-                newDocument->registerNodeList(list);
+                oldDocument.unregisterNodeList(list);
+                newDocument.registerNodeList(list);
             }
 
             TagNodeListCacheNS::const_iterator tagEnd = m_tagNodeListCacheNS.end();
             for (TagNodeListCacheNS::const_iterator it = m_tagNodeListCacheNS.begin(); it != tagEnd; ++it) {
                 LiveNodeListBase* list = it->value;
                 ASSERT(!list->isRootedAtDocument());
-                oldDocument->unregisterNodeList(list);
-                newDocument->registerNodeList(list);
+                oldDocument.unregisterNodeList(list);
+                newDocument.registerNodeList(list);
             }
         }
     }
 
 private:
     NodeListsNodeData()
         : m_childNodeList(0)
     { }
 
     std::pair<unsigned char, AtomicString> namedNodeListKey(CollectionType type, const AtomicString& name)
@@ skipping 84 matching lines @@
     ownerNode->clearNodeLists();
     return true;
 }
 
 // Ensure the 10 bits reserved for the m_connectedFrameCount cannot overflow
 COMPILE_ASSERT(Page::maxNumberOfFrames < 1024, Frame_limit_should_fit_in_rare_data_count);
 
 } // namespace WebCore
 
 #endif // NodeRareData_h