Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/CSSDefaultStyleSheets.cpp

Index: Source/core/css/CSSDefaultStyleSheets.cpp
diff --git a/Source/core/css/CSSDefaultStyleSheets.cpp b/Source/core/css/CSSDefaultStyleSheets.cpp
index 35099aba19fc312f28159ce1e48d8e444126b7a1..699285e8c81b37f39ac2c8ade5796e88af6a29a5 100644
--- a/Source/core/css/CSSDefaultStyleSheets.cpp
+++ b/Source/core/css/CSSDefaultStyleSheets.cpp
@@ -86,12 +86,12 @@ CSSDefaultStyleSheets::CSSDefaultStyleSheets()
     , m_defaultPrintStyle(0)
     , m_defaultViewSourceStyle(0)
     , m_defaultXHTMLMobileProfileStyle(0)
-    , m_defaultStyleSheet(0)
-    , m_viewportStyleSheet(0)
-    , m_quirksStyleSheet(0)
-    , m_svgStyleSheet(0)
-    , m_mediaControlsStyleSheet(0)
-    , m_fullscreenStyleSheet(0)
+    , m_defaultStyleSheet(nullptr)
+    , m_viewportStyleSheet(nullptr)
+    , m_quirksStyleSheet(nullptr)
+    , m_svgStyleSheet(nullptr)
+    , m_mediaControlsStyleSheet(nullptr)
+    , m_fullscreenStyleSheet(nullptr)
 {
     m_defaultStyle = RuleSet::create().leakPtr();
     m_defaultViewportStyle = RuleSet::create().leakPtr();