WIP (Introduce WTF::NonNullPtr<T>.)

Source/core/css/resolver/ScopedStyleResolver.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 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:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 37 matching lines @@
 
 // This class selects a RenderStyle for a given element based on a collection of stylesheets.
 class ScopedStyleResolver {
     WTF_MAKE_NONCOPYABLE(ScopedStyleResolver); WTF_MAKE_FAST_ALLOCATED;
 public:
     static PassOwnPtr<ScopedStyleResolver> create(const ContainerNode& scopingNode) { return adoptPtr(new ScopedStyleResolver(scopingNode)); }
 
     static const ContainerNode* scopingNodeFor(const CSSStyleSheet*);
 
     const ContainerNode& scopingNode() const { return m_scopingNode; }
-    const TreeScope& treeScope() const { return m_scopingNode.treeScope(); }
+    NonNullPtr<const TreeScope> treeScope() const { return m_scopingNode.treeScope(); }
     void prepareEmptyRuleSet() { m_authorStyle = RuleSet::create(); }
     void setParent(ScopedStyleResolver* newParent) { m_parent = newParent; }
     ScopedStyleResolver* parent() { return m_parent; }
 
     bool hasOnlyEmptyRuleSets() const { return !m_authorStyle->ruleCount() && m_atHostRules.isEmpty(); }
 
 public:
     bool checkRegionStyle(Element*);
     const StyleRuleKeyframes* keyframeStylesForAnimation(const StringImpl* animationName);
     void addKeyframeStyle(PassRefPtr<StyleRuleKeyframes>);
@@ skipping 84 matching lines @@
 {
     if (!cacheIsValid(element))
         resolveStyleCache(element);
 
     return m_cache.scopedResolver;
 }
 
 } // namespace WebCore
 
 #endif // ScopedStyleResolver_h