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

Source/core/animation/css/CSSAnimations.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 810 matching lines @@
     case CSSPropertyWebkitTransitionProperty:
     case CSSPropertyWebkitTransitionTimingFunction:
         return false;
     default:
         return true;
     }
 }
 
 void CSSAnimations::trace(Visitor* visitor)
 {
-#if ENABLE(OILPAN)
     visitor->trace(m_transitions);
     visitor->trace(m_pendingUpdate);
     visitor->trace(m_animations);
     visitor->trace(m_previousActiveInterpolationsForAnimations);
-#endif
 }
 
 void CSSAnimationUpdate::trace(Visitor* visitor)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_newTransitions);
     visitor->trace(m_activeInterpolationsForAnimations);
     visitor->trace(m_activeInterpolationsForTransitions);
     visitor->trace(m_newAnimations);
     visitor->trace(m_cancelledAnimationPlayers);
 #endif
 }
 
 } // namespace blink