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

Source/core/html/track/WebVTTElement.cpp

 /*
  * Copyright (C) 2013 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 100 matching lines @@
         htmlElement = HTMLElement::create(HTMLNames::rtTag, document);
         break;
     default:
         ASSERT_NOT_REACHED();
     }
 
     htmlElement.get()->setAttribute(HTMLNames::classAttr, getAttribute(HTMLNames::classAttr));
     return htmlElement;
 }
 
+void WebVTTElement::acceptHeapVisitor(Visitor* visitor) const
+{
+    Element::acceptHeapVisitor(visitor);
+}
+
 } // namespace WebCore