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

Source/core/dom/DocumentMarkerController.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 460 matching lines @@
                 result.append(marker->renderedRect());
             }
         }
     }
 
     return result;
 }
 
 void DocumentMarkerController::trace(Visitor* visitor)
 {
-#if ENABLE(OILPAN)
     visitor->trace(m_markers);
-#endif
 }
 
 void DocumentMarkerController::removeMarkers(Node* node, DocumentMarker::MarkerTypes markerTypes)
 {
     if (!possiblyHasMarkers(markerTypes))
         return;
     ASSERT(!m_markers.isEmpty());
 
     MarkerMap::iterator iterator = m_markers.find(node);
     if (iterator != m_markers.end())
@@ skipping 235 matching lines @@
 
 } // namespace blink
 
 #ifndef NDEBUG
 void showDocumentMarkers(const blink::DocumentMarkerController* controller)
 {
     if (controller)
         controller->showMarkers();
 }
 #endif