Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/scroll/ScrollView.cpp

Index: Source/platform/scroll/ScrollView.cpp
diff --git a/Source/platform/scroll/ScrollView.cpp b/Source/platform/scroll/ScrollView.cpp
index 6e14d87d4077181f723d4b75296f1249ad1eea3a..a9bbb1ea0e1fed9cc53693355eed1563fdc0a00c 100644
--- a/Source/platform/scroll/ScrollView.cpp
+++ b/Source/platform/scroll/ScrollView.cpp
@@ -81,7 +81,7 @@ void ScrollView::setHasHorizontalScrollbar(bool hasBar)
     } else if (!hasBar && m_horizontalScrollbar) {
         willRemoveScrollbar(m_horizontalScrollbar.get(), HorizontalScrollbar);
         removeChild(m_horizontalScrollbar.get());
-        m_horizontalScrollbar = 0;
+        m_horizontalScrollbar = nullptr;
     }
 }
 
@@ -95,7 +95,7 @@ void ScrollView::setHasVerticalScrollbar(bool hasBar)
     } else if (!hasBar && m_verticalScrollbar) {
         willRemoveScrollbar(m_verticalScrollbar.get(), VerticalScrollbar);
         removeChild(m_verticalScrollbar.get());
-        m_verticalScrollbar = 0;
+        m_verticalScrollbar = nullptr;
     }
 }