Oilpan: fix build after r202625.

Source/core/css/CSSImageSetValue.cpp

 /*
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 175 matching lines @@
 {
     visitor->trace(m_imageSet);
     CSSValueList::traceAfterDispatch(visitor);
 }
 
 PassRefPtrWillBeRawPtr<CSSImageSetValue> CSSImageSetValue::valueWithURLsMadeAbsolute()
 {
     CSSImageSetValue* value = CSSImageSetValue::create().get();
     for (auto& item : *this)
         item->isImageValue() ? value->append(toCSSImageValue(*item).valueWithURLMadeAbsolute()) : value->append(item);
-    return adoptRef(value);
+    return adoptRefWillBeNoop(value);
 }
 
 
 } // namespace blink