Oilpan: avoid using WeakPtr<> for heap residing objects.

Source/core/html/FormAssociatedElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 144 matching lines @@
     if (m_form)
         m_form->disassociate(*this);
     if (newForm) {
 #if ENABLE(OILPAN)
         m_form = newForm;
 #else
         m_form = newForm->createWeakPtr();
 #endif
         m_form->associate(*this);
     } else {
-#if ENABLE(OILPAN)
         m_form = nullptr;
-#else
-        m_form = WeakPtr<HTMLFormElement>();
-#endif
     }
     didChangeForm();
 }
 
 void FormAssociatedElement::willChangeForm()
 {
 }
 
 void FormAssociatedElement::didChangeForm()
 {
@@ skipping 173 matching lines @@
     visitor->trace(m_element);
     IdTargetObserver::trace(visitor);
 }
 
 void FormAttributeTargetObserver::idTargetChanged()
 {
     m_element->formAttributeTargetChanged();
 }
 
 } // namespace blink