Oilpan: Remove support for tracing of off-heap ListHashSets.

Source/core/css/FontFaceCache.cpp

 /*
  * Copyright (C) 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * 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 198 matching lines @@
                 continue;
             if (!faceResult.storedValue->value || compareFontFaces(candidate, faceResult.storedValue->value.get(), traits))
                 faceResult.storedValue->value = candidate;
         }
     }
     return faceResult.storedValue->value.get();
 }
 
 void FontFaceCache::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_fontFaces);
     visitor->trace(m_fonts);
     visitor->trace(m_styleRuleToFontFace);
     visitor->trace(m_cssConnectedFontFaces);
+#endif
 }
 
 }