Revert of Move all RefPtr's to CSSValue to oilpan transition types, except for the one in CSSCursorImageValue.

Source/core/css/CSSProperty.h

Index: Source/core/css/CSSProperty.h
diff --git a/Source/core/css/CSSProperty.h b/Source/core/css/CSSProperty.h
index 4f6a40c61737c68b0365542dce3d9bf0fa7e6ac0..00244680aa4e815d4d3812535ace413a0bed123c 100644
--- a/Source/core/css/CSSProperty.h
+++ b/Source/core/css/CSSProperty.h
@@ -53,7 +53,6 @@
 };
 
 class CSSProperty {
-    ALLOW_ONLY_INLINE_ALLOCATION();
 public:
     CSSProperty(CSSPropertyID propertyID, PassRefPtrWillBeRawPtr<CSSValue> value, bool important = false, bool isSetFromShorthand = false, int indexInShorthandsVector = 0, bool implicit = false)
         : m_metadata(propertyID, isSetFromShorthand, indexInShorthandsVector, important, implicit, isInheritedProperty(propertyID))
@@ -82,11 +81,9 @@
 
     const StylePropertyMetadata& metadata() const { return m_metadata; }
 
-    void trace(Visitor* visitor) { visitor->trace(m_value); }
-
 private:
     StylePropertyMetadata m_metadata;
-    RefPtrWillBeMember<CSSValue> m_value;
+    RefPtr<CSSValue> m_value;
 };
 
 inline CSSPropertyID prefixingVariantForPropertyId(CSSPropertyID propId)