Revert of [oilpan]: Remove support for tracing off-heap hashmaps.

Source/core/html/HTMLCollection.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Samsung Electronics. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 66 matching lines @@
             return adoptPtrWillBeNoop(new NamedItemCache);
         }
 
         WillBeHeapVector<RawPtrWillBeMember<Element> >* getElementsById(const AtomicString& id) const { return m_idCache.get(id.impl()); }
         WillBeHeapVector<RawPtrWillBeMember<Element> >* getElementsByName(const AtomicString& name) const { return m_nameCache.get(name.impl()); }
         void addElementWithId(const AtomicString& id, Element* element) { addElementToMap(m_idCache, id, element); }
         void addElementWithName(const AtomicString& name, Element* element) { addElementToMap(m_nameCache, name, element); }
 
         void trace(Visitor* visitor)
         {
-#if ENABLE(OILPAN)
             visitor->trace(m_idCache);
             visitor->trace(m_nameCache);
-#endif
         }
 
     private:
         NamedItemCache();
         typedef WillBeHeapHashMap<StringImpl*, OwnPtrWillBeMember<WillBeHeapVector<RawPtrWillBeMember<Element> > > > StringToElementsMap;
         static void addElementToMap(StringToElementsMap& map, const AtomicString& key, Element* element)
         {
             OwnPtrWillBeMember<WillBeHeapVector<RawPtrWillBeMember<Element> > >& vector = map.add(key.impl(), nullptr).storedValue->value;
             if (!vector)
                 vector = adoptPtrWillBeNoop(new WillBeHeapVector<RawPtrWillBeMember<Element> >);
@@ skipping 57 matching lines @@
 {
     if (!attrName || shouldInvalidateTypeOnAttributeChange(invalidationType(), *attrName))
         invalidateCache();
     else if (*attrName == HTMLNames::idAttr || *attrName == HTMLNames::nameAttr)
         invalidateIdNameCacheMaps();
 }
 
 } // namespace
 
 #endif