[oilpan] The Node hierarchy should have correct accept method chains

Source/core/dom/DocumentType.h

Index: Source/core/dom/DocumentType.h
diff --git a/Source/core/dom/DocumentType.h b/Source/core/dom/DocumentType.h
index dbf3b13e5a66db67ec41f98608dbbbd290a1407b..9d1eb37a60ea89437c4a555452354e7d72a1ca80 100644
--- a/Source/core/dom/DocumentType.h
+++ b/Source/core/dom/DocumentType.h
@@ -43,6 +43,8 @@ public:
     const String& systemId() const { return m_systemId; }
     const String& internalSubset() const { return m_subset; }
 
+    virtual void acceptHeapVisitor(Visitor*) const OVERRIDE;
+
 private:
     DocumentType(Handle<Document>, const String& name, const String& publicId, const String& systemId);