Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/rendering/RenderScrollbar.cpp

Index: Source/core/rendering/RenderScrollbar.cpp
diff --git a/Source/core/rendering/RenderScrollbar.cpp b/Source/core/rendering/RenderScrollbar.cpp
index f2f7a89fbf0ad8527309c8ff1ebc32fe8d70e263..86b05f97b4d7dc22f3c151630623a8b7dec8f81b 100644
--- a/Source/core/rendering/RenderScrollbar.cpp
+++ b/Source/core/rendering/RenderScrollbar.cpp
@@ -148,7 +148,7 @@ void RenderScrollbar::setPressedPart(ScrollbarPart part)
 PassRefPtr<RenderStyle> RenderScrollbar::getScrollbarPseudoStyle(ScrollbarPart partType, PseudoId pseudoId)
 {
     if (!owningRenderer())
-        return 0;
+        return nullptr;
 
     RefPtr<RenderStyle> result = owningRenderer()->getUncachedPseudoStyle(PseudoStyleRequest(pseudoId, this, partType), owningRenderer()->style());
     // Scrollbars for root frames should always have background color
@@ -223,7 +223,7 @@ void RenderScrollbar::updateScrollbarPart(ScrollbarPart partType, bool destroy)
     if (partType == NoPart)
         return;
 
-    RefPtr<RenderStyle> partStyle = !destroy ? getScrollbarPseudoStyle(partType,  pseudoForScrollbarPart(partType)) : PassRefPtr<RenderStyle>(0);
+    RefPtr<RenderStyle> partStyle = !destroy ? getScrollbarPseudoStyle(partType,  pseudoForScrollbarPart(partType)) : PassRefPtr<RenderStyle>(nullptr);
 
     bool needRenderer = !destroy && partStyle && partStyle->display() != NONE && partStyle->visibility() == VISIBLE;