Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/mhtml/ArchiveResource.cpp

Index: Source/platform/mhtml/ArchiveResource.cpp
diff --git a/Source/platform/mhtml/ArchiveResource.cpp b/Source/platform/mhtml/ArchiveResource.cpp
index e79cba255b6a626a9523b16388ac087fef8ab8d3..46b899ec3e200446e1cc1fae2bed3bffbdce4a7a 100644
--- a/Source/platform/mhtml/ArchiveResource.cpp
+++ b/Source/platform/mhtml/ArchiveResource.cpp
@@ -45,7 +45,7 @@ inline ArchiveResource::ArchiveResource(PassRefPtr<SharedBuffer> data, const KUR
 PassRefPtr<ArchiveResource> ArchiveResource::create(PassRefPtr<SharedBuffer> data, const KURL& url, const AtomicString& mimeType, const AtomicString& textEncoding, const String& frameName, const ResourceResponse& response)
 {
     if (!data)
-        return 0;
+        return nullptr;
     if (response.isNull()) {
         unsigned dataSize = data->size();
         return adoptRef(new ArchiveResource(data, url, mimeType, textEncoding, frameName,