Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/html/ImageData.cpp

Index: Source/core/html/ImageData.cpp
diff --git a/Source/core/html/ImageData.cpp b/Source/core/html/ImageData.cpp
index 64c86c931b6c29d2021f87ccde7304f922eb6cd6..bcba908180f35739d9b4140b77e6a1d7968b8a86 100644
--- a/Source/core/html/ImageData.cpp
+++ b/Source/core/html/ImageData.cpp
@@ -37,7 +37,7 @@ PassRefPtr<ImageData> ImageData::create(const IntSize& size)
     dataSize *= size.width();
     dataSize *= size.height();
     if (dataSize.hasOverflowed())
-        return 0;
+        return nullptr;
 
     return adoptRef(new ImageData(size));
 }
@@ -48,11 +48,11 @@ PassRefPtr<ImageData> ImageData::create(const IntSize& size, PassRefPtr<Uint8Cla
     dataSize *= size.width();
     dataSize *= size.height();
     if (dataSize.hasOverflowed())
-        return 0;
+        return nullptr;
 
     if (dataSize.unsafeGet() < 0
         || static_cast<unsigned>(dataSize.unsafeGet()) > byteArray->length())
-        return 0;
+        return nullptr;
 
     return adoptRef(new ImageData(size, byteArray));
 }