Move most of the [Pass]RefPtr's of CSSPrimitiveValue to our transition types.

Source/core/animation/AnimatableLength.h

 /*
  * 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 96 matching lines @@
     {
         return m_unitType == UnitTypeViewportWidth || m_unitType == UnitTypeViewportHeight || m_unitType == UnitTypeViewportMin || m_unitType == UnitTypeViewportMax;
     }
 
     static PassRefPtr<AnimatableLength> create(const AnimatableLength* leftAddend, const AnimatableLength* rightAddend)
     {
         ASSERT(leftAddend && rightAddend);
         return create(CSSCalcValue::createExpressionNode(leftAddend->toCSSCalcExpressionNode(), rightAddend->toCSSCalcExpressionNode(), CalcAdd));
     }
 
-    PassRefPtr<CSSPrimitiveValue> toCSSPrimitiveValue(NumberRange) const;
+    PassRefPtrWillBeRawPtr<CSSPrimitiveValue> toCSSPrimitiveValue(NumberRange) const;
     PassRefPtr<CSSCalcExpressionNode> toCSSCalcExpressionNode() const;
 
     PassRefPtr<AnimatableLength> scale(double) const;
     double clampedNumber(NumberRange range) const
     {
         ASSERT(!isCalc());
         return (range == NonNegativeValues && m_number <= 0) ? 0 : m_number;
     }
 
     // Returns true and populates numberType, if primitiveUnit is a primitive length unit. Otherwise, returns false.
@@ skipping 20 matching lines @@
             return m_unitType;
 
         return UnitTypeCalc;
     }
 
     double m_number;
     const NumberUnitType m_unitType;
 
     RefPtr<CSSCalcExpressionNode> m_calcExpression;
 
-    mutable RefPtr<CSSPrimitiveValue> m_cachedCSSPrimitiveValue;
+    mutable RefPtrWillBePersistent<CSSPrimitiveValue> m_cachedCSSPrimitiveValue;
 
     friend class AnimationAnimatableLengthTest;
 };
 
 DEFINE_ANIMATABLE_VALUE_TYPE_CASTS(AnimatableLength, isLength());
 
 } // namespace WebCore
 
 #endif // AnimatableLength_h