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

Source/core/animation/ActiveAnimations.cpp

 /*
  * 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 75 matching lines @@
 }
 
 void ActiveAnimations::cancelAnimationOnCompositor()
 {
     for (AnimationPlayerCountedSet::iterator it = m_players.begin(); it != m_players.end(); ++it)
         it->key->cancelAnimationOnCompositor();
 }
 
 void ActiveAnimations::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_cssAnimations);
     visitor->trace(m_defaultStack);
     visitor->trace(m_players);
+#endif
 }
 
 } // namespace blink