Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/resolver/ViewportStyleResolver.cpp

Index: Source/core/css/resolver/ViewportStyleResolver.cpp
diff --git a/Source/core/css/resolver/ViewportStyleResolver.cpp b/Source/core/css/resolver/ViewportStyleResolver.cpp
index 120f3b7a0bb3e2caa245788116733a68683ff79c..2db7f8b3a9c79b3c3b1c10d3b0dfdf0fe9e6149b 100644
--- a/Source/core/css/resolver/ViewportStyleResolver.cpp
+++ b/Source/core/css/resolver/ViewportStyleResolver.cpp
@@ -96,7 +96,7 @@ void ViewportStyleResolver::resolve()
 
     if (!m_propertySet || (!m_hasAuthorStyle && m_document->hasLegacyViewportTag())) {
         ASSERT(!m_hasAuthorStyle);
-        m_propertySet = 0;
+        m_propertySet = nullptr;
         m_document->setViewportDescription(ViewportDescription());
         return;
     }
@@ -115,7 +115,7 @@ void ViewportStyleResolver::resolve()
 
     m_document->setViewportDescription(description);
 
-    m_propertySet = 0;
+    m_propertySet = nullptr;
     m_hasAuthorStyle = false;
 }