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

Source/core/dom/TreeScope.h

 /*
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 46 matching lines @@
     void setParentTreeScope(TreeScope*);
 
     Element* adjustedFocusedElement() const;
     Element* getElementById(const AtomicString&) const;
     const Vector<Element*>& getAllElementsById(const AtomicString&) const;
     bool hasElementWithId(StringImpl* id) const;
     bool containsMultipleElementsWithId(const AtomicString& id) const;
     void addElementById(const AtomicString& elementId, Element*);
     void removeElementById(const AtomicString& elementId, Element*);
 
-    Document* documentScope() const { return m_documentScope; }
+    Document& documentScope() const
+    {
+        ASSERT(m_documentScope);
+        return *m_documentScope;
+    }
 
     Node* ancestorInThisScope(Node*) const;
 
     void addImageMap(HTMLMapElement*);
     void removeImageMap(HTMLMapElement*);
     HTMLMapElement* getImageMap(const String& url) const;
 
     Element* elementFromPoint(int x, int y) const;
 
     // For accessibility.
@@ skipping 50 matching lines @@
 
     const KURL& baseURL() const { return m_baseURL; }
     KURL completeURL(const String&) const;
 
 protected:
     TreeScope(ContainerNode*, Document*);
     TreeScope(Document*);
     virtual ~TreeScope();
 
     void destroyTreeScopeData();
-    void clearDocumentScope();
-    void setDocumentScope(Document* document)
-    {
-        ASSERT(document);
-        m_documentScope = document;
-    }
+    void setDocumentScope(Document& document) { m_documentScope = &document; }
 
     bool hasGuardRefCount() const { return m_guardRefCount; }
 
     void setNeedsStyleRecalcForViewportUnits();
 
     void setBaseURL(const KURL& baseURL) { m_baseURL = baseURL; }
 
 private:
-    TreeScope();
-
     virtual void dispose() { }
 
     int refCount() const;
 #if SECURITY_ASSERT_ENABLED
     bool deletionHasBegun();
     void beginDeletion();
 #else
     bool deletionHasBegun() { return false; }
     void beginDeletion() { }
 #endif
@@ skipping 33 matching lines @@
 inline bool operator!=(const TreeScope& a, const TreeScope& b) { return !(a == b); }
 inline bool operator!=(const TreeScope& a, const TreeScope* b) { return !(a == b); }
 inline bool operator!=(const TreeScope* a, const TreeScope& b) { return !(a == b); }
 
 RenderObject* rendererFromPoint(Document*, int x, int y, LayoutPoint* localPoint = 0);
 TreeScope* commonTreeScope(Node*, Node*);
 
 } // namespace WebCore
 
 #endif // TreeScope_h