Oilpan: Replace RefPtrs to Node and its subclasses in core/dom/ with Oilpan transtion types.

Source/core/dom/IncrementLoadEventDelayCount.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IncrementLoadEventDelayCount_h
 #define IncrementLoadEventDelayCount_h
 
+#include "platform/heap/Handle.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/RefPtr.h"
 
 namespace WebCore {
 
 class Document;
 
 // A helper class that will increment a document's loadEventDelayCount on
 // contruction and decrement it on destruction (semantics similar to RefPtr).
 class IncrementLoadEventDelayCount {
     WTF_MAKE_NONCOPYABLE(IncrementLoadEventDelayCount);
 
 public:
     IncrementLoadEventDelayCount(Document&);
     ~IncrementLoadEventDelayCount();
 
     // Increments the new document's count and decrements the old count.
     void documentChanged(Document& newDocument);
 
 private:
-    RefPtr<Document> m_document;
+    RefPtrWillBePersistent<Document> m_document;
 };
 }
 
 #endif