Oilpan: fix build++ after r192490.

Source/core/html/HTMLIFrameElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Simon Hausmann (hausmann@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2006, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Ericsson AB. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 32 matching lines @@
     , m_sandbox(DOMSettableTokenList::create(this))
 {
 }
 
 DEFINE_NODE_FACTORY(HTMLIFrameElement)
 
 DEFINE_TRACE(HTMLIFrameElement)
 {
     visitor->trace(m_sandbox);
     HTMLFrameElementBase::trace(visitor);
+    DOMSettableTokenListObserver::trace(visitor);
 }
 
 HTMLIFrameElement::~HTMLIFrameElement()
 {
+#if !ENABLE(OILPAN)
     m_sandbox->setObserver(nullptr);
+#endif
 }
 
 DOMSettableTokenList* HTMLIFrameElement::sandbox() const
 {
     return m_sandbox.get();
 }
 
 bool HTMLIFrameElement::isPresentationAttribute(const QualifiedName& name) const
 {
     if (name == widthAttr || name == heightAttr || name == alignAttr || name == frameborderAttr)
@@ skipping 94 matching lines @@
 
 void HTMLIFrameElement::valueChanged()
 {
     String invalidTokens;
     setSandboxFlags(m_sandbox->value().isNull() ? SandboxNone : parseSandboxPolicy(m_sandbox->tokens(), invalidTokens));
     if (!invalidTokens.isNull())
         document().addConsoleMessage(ConsoleMessage::create(OtherMessageSource, ErrorMessageLevel, "Error while parsing the 'sandbox' attribute: " + invalidTokens));
 }
 
 }