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

Source/core/dom/TreeScope.cpp

 /*
  * 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 62 matching lines @@
     : m_rootNode(document)
     , m_documentScope(document)
     , m_parentTreeScope(0)
     , m_guardRefCount(0)
     , m_idTargetObserverRegistry(IdTargetObserverRegistry::create())
 {
     ASSERT(document);
     m_rootNode->setTreeScope(this);
 }
 
-TreeScope::TreeScope()
-    : m_rootNode(0)
-    , m_documentScope(0)
-    , m_parentTreeScope(0)
-    , m_guardRefCount(0)
-{
-}
-
 TreeScope::~TreeScope()
 {
     ASSERT(!m_guardRefCount);
     m_rootNode->setTreeScope(0);
 
     if (m_selection) {
         m_selection->clearTreeScope();
         m_selection = 0;
     }
 
     if (m_parentTreeScope)
         m_parentTreeScope->guardDeref();
 }
 
 bool TreeScope::rootNodeHasTreeSharedParent() const
 {
     return rootNode()->hasTreeSharedParent();
 }
 
 void TreeScope::destroyTreeScopeData()
 {
     m_elementsById.clear();
     m_imageMapsByName.clear();
     m_labelsByForAttribute.clear();
 }
 
-void TreeScope::clearDocumentScope()
-{
-    ASSERT(rootNode()->isDocumentNode());
-    m_documentScope = 0;
-}
-
 void TreeScope::setParentTreeScope(TreeScope* newParentScope)
 {
     // A document node cannot be re-parented.
     ASSERT(!rootNode()->isDocumentNode());
     // Every scope other than document needs a parent scope.
     ASSERT(newParentScope);
 
     newParentScope->guardRef();
     if (m_parentTreeScope)
         m_parentTreeScope->guardDeref();
@@ skipping 373 matching lines @@
         for (ShadowRoot* root = element->youngestShadowRoot(); root; root = root->olderShadowRoot())
             root->setNeedsStyleRecalcForViewportUnits();
         RenderStyle* style = element->renderStyle();
         if (style && style->hasViewportUnits())
             element->setNeedsStyleRecalc(LocalStyleChange);
     }
 }
 
 KURL TreeScope::completeURL(const String& url) const
 {
-    ASSERT(documentScope());
-    return documentScope()->completeURLWithOverride(url, baseURL());
+    return documentScope().completeURLWithOverride(url, baseURL());
 }
 
 } // namespace WebCore