[Oilpan] Migrate most classes under core/animations to Oilpan heap.

Source/core/animation/animatable/AnimatableDouble.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 18 matching lines @@
  */
 
 #include "config.h"
 #include "core/animation/animatable/AnimatableDouble.h"
 
 #include "platform/animation/AnimationUtilities.h"
 #include <math.h>
 
 namespace blink {
 
-PassRefPtrWillBeRawPtr<AnimatableValue> AnimatableDouble::interpolateTo(const AnimatableValue* value, double fraction) const
+AnimatableValue* AnimatableDouble::interpolateTo(const AnimatableValue* value, double fraction) const
 {
     const AnimatableDouble* other = toAnimatableDouble(value);
     return AnimatableDouble::create(blend(m_number, other->m_number, fraction));
 }
 
 bool AnimatableDouble::equalTo(const AnimatableValue* value) const
 {
     return m_number == toAnimatableDouble(value)->m_number;
 }
 
 } // namespace blink