Oilpan: Remove most WillBe types from the code base

third_party/WebKit/Source/core/animation/ConstantStyleInterpolation.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ConstantStyleInterpolation_h
 #define ConstantStyleInterpolation_h
 
 #include "core/animation/StyleInterpolation.h"
 #include "core/css/resolver/StyleBuilder.h"
 
@@ skipping 10 matching lines @@
     {
         StyleBuilder::applyProperty(m_id, state, m_value.get());
     }
 
 private:
     ConstantStyleInterpolation(CSSValue* value, CSSPropertyID id)
         : StyleInterpolation(InterpolableList::create(0), InterpolableList::create(0), id)
         , m_value(value)
     { }
 
-    RefPtrWillBePersistent<CSSValue> m_value;
+    Persistent<CSSValue> m_value;
 };
 
 } // namespace blink
 
 #endif