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

Source/core/dom/StyleSheetCollections.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 96 matching lines @@
     void resetCSSFeatureFlags(const RuleFeatureSet&);
 
     void didModifySeamlessParentStyleSheet() { m_needsDocumentStyleSheetsUpdate = true; }
     void didRemoveShadowRoot(ShadowRoot*);
     void appendActiveAuthorStyleSheets(StyleResolver*);
     void getActiveAuthorStyleSheets(Vector<const Vector<RefPtr<CSSStyleSheet> >*>& activeAuthorStyleSheets) const;
 
 private:
     StyleSheetCollections(Document&);
 
-    StyleSheetCollection* ensureStyleSheetCollectionFor(TreeScope&);
-    StyleSheetCollection* styleSheetCollectionFor(TreeScope&);
+    StyleSheetCollection* ensureStyleSheetCollectionFor(NonNullPtr<TreeScope>);
+    StyleSheetCollection* styleSheetCollectionFor(NonNullPtr<TreeScope>);
     void activeStyleSheetsUpdatedForInspector();
     bool shouldUpdateShadowTreeStyleSheetCollection(StyleResolverUpdateMode);
 
     typedef ListHashSet<TreeScope*, 16> TreeScopeSet;
     static void insertTreeScopeInDocumentOrder(TreeScopeSet&, TreeScope*);
 
     Document& m_document;
 
     // Track the number of currently loading top-level stylesheets needed for rendering.
     // Sheets loaded using the @import directive are not included in this count.
@@ skipping 25 matching lines @@
     bool m_usesSiblingRules;
     bool m_usesSiblingRulesOverride;
     bool m_usesFirstLineRules;
     bool m_usesFirstLetterRules;
     bool m_usesRemUnits;
 };
 
 }
 
 #endif