Oilpan: Remove support for tracing off-heap HashSets.

Source/core/css/CSSFontSelector.cpp

 /*
  * Copyright (C) 2007, 2008, 2011 Apple Inc. All rights reserved.
  *           (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 156 matching lines @@
 {
     if (!document.settings())
         return;
     m_genericFontFamilySettings = document.settings()->genericFontFamilySettings();
     // Need to increment FontFaceCache version to update RenderStyles.
     m_fontFaceCache.incrementVersion();
 }
 
 void CSSFontSelector::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_document);
     visitor->trace(m_fontFaceCache);
     visitor->trace(m_clients);
     visitor->trace(m_fontLoader);
+#endif
     FontSelector::trace(visitor);
 }
 
 }