Cleanup dart to string conversions.

Source/WebCore/bindings/dart/custom/DartDOMStringListCustom.cpp

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "config.h"
 #include "DartDOMStringList.h"
 
 #include <wtf/Vector.h>
 
 namespace WebCore {
 
 PassRefPtr<DOMStringList> DartDOMStringList::toNative(Dart_Handle handle, Dart_Handle& exception)
 {
     if (DartDOMWrapper::instanceOf<DartDOMStringList>(handle))
         return DartDOMWrapper::unwrapDartWrapper<DartDOMStringList>(handle, exception);
 
     Vector<Dart_Handle> elements;
     DartUtilities::extractListElements(handle, exception, elements);
     if (exception)
         return 0;
 
     RefPtr<DOMStringList> m_domStringList = DOMStringList::create();
     for (size_t i = 0; i < elements.size(); i++) {
-        RefPtr<StringImpl> element = DartUtilities::toStringImpl(elements[i], DartUtilities::ConvertNone, exception);
+        DartStringAdapter element = DartUtilities::dartToString(elements[i], exception);
         if (exception)
             return 0;
-        ASSERT(element.get());
-        m_domStringList->append(element.get());
+        m_domStringList->append(element);
     }
     return m_domStringList.release();
 }
 
 }