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

Source/core/css/RuleSet.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 361 matching lines @@
     visitor->trace(m_rule);
 }
 
 void RuleData::trace(Visitor* visitor)
 {
     visitor->trace(m_rule);
 }
 
 void RuleSet::PendingRuleMaps::trace(Visitor* visitor)
 {
-#if ENABLE(OILPAN)
     visitor->trace(idRules);
     visitor->trace(classRules);
     visitor->trace(tagRules);
     visitor->trace(shadowPseudoElementRules);
-#endif
 }
 
 void RuleSet::trace(Visitor* visitor)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_idRules);
     visitor->trace(m_classRules);
     visitor->trace(m_tagRules);
     visitor->trace(m_shadowPseudoElementRules);
     visitor->trace(m_linkPseudoClassRules);
@@ skipping 17 matching lines @@
 
 #ifndef NDEBUG
 void RuleSet::show()
 {
     for (WillBeHeapVector<RuleData>::const_iterator it = m_allRules.begin(); it != m_allRules.end(); ++it)
         it->selector().show();
 }
 #endif
 
 } // namespace blink