Incorporating review feedback from https://codereview.chromium.org/24294002/

Source/bindings/dart/DartCustomElementWrapper.cpp

 /*
  * Copyright (C) 2012 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 79 matching lines @@
         return createUpgradeCandidateWrapper(element.get(), createSpecificWrapper);
 
     return upgradeDartWrapper(element.get());
 }
 
 template<>
 Dart_Handle DartCustomElementWrapper<HTMLElement>::upgradeDartWrapper(HTMLElement* element)
 {
     DartDOMData* domData = DartDOMData::current();
     DartCustomElementBinding* binding = domData->customElementBinding(CustomElement::definitionFor(element));
-    Dart_Handle customType = binding->customType();
+    Dart_Handle customType = Dart_HandleFromPersistent(binding->customType());
     ASSERT(!Dart_IsError(customType));
 
     Dart_WeakPersistentHandle oldInstance = DartDOMWrapper::lookupWrapper(DartHTMLElement::isNode, reinterpret_cast<HTMLElement*>(element));
     if (oldInstance)
         DartDOMWrapper::disassociateWrapper<DartHTMLElement>(reinterpret_cast<HTMLElement*>(element), Dart_HandleFromWeakPersistent(oldInstance));
 
     Dart_Handle newInstance = Dart_Allocate(customType);
     ASSERT(!Dart_IsError(newInstance));
 
     Dart_Handle result = Dart_SetNativeInstanceField(newInstance, 0, reinterpret_cast<intptr_t>(element));
@@ skipping 13 matching lines @@
     return Dart_Handle();
 }
 
 template
 class DartCustomElementWrapper<HTMLElement>;
 
 template
 class DartCustomElementWrapper<SVGElement>;
 
 } // namespace WebCore