Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/dom/StyleEngine.cpp

 /*
  * 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, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 67 matching lines @@
     , m_usesSiblingRules(false)
     , m_usesSiblingRulesOverride(false)
     , m_usesFirstLineRules(false)
     , m_usesFirstLetterRules(false)
     , m_usesRemUnits(false)
     , m_maxDirectAdjacentSelectors(0)
     , m_ignorePendingStylesheets(false)
     , m_didCalculateResolver(false)
     // We don't need to create CSSFontSelector for imported document or
     // HTMLTemplateElement's document, because those documents have no frame.
-    , m_fontSelector(document.frame() ? CSSFontSelector::create(&document) : 0)
+    , m_fontSelector(document.frame() ? CSSFontSelector::create(&document) : nullptr)
 {
 }
 
 StyleEngine::~StyleEngine()
 {
     for (unsigned i = 0; i < m_injectedAuthorStyleSheets.size(); ++i)
         m_injectedAuthorStyleSheets[i]->clearOwnerNode();
     for (unsigned i = 0; i < m_authorStyleSheets.size(); ++i)
         m_authorStyleSheets[i]->clearOwnerNode();
 
@@ skipping 511 matching lines @@
 {
     HashMap<StyleSheetContents*, AtomicString>::iterator it = sheetToTextCache().find(contents);
     if (it == sheetToTextCache().end())
         return;
 
     textToSheetCache().remove(it->value);
     sheetToTextCache().remove(contents);
 }
 
 }