Fixing another case of multiple upgrades of a custom element

Source/bindings/dart/DartDOMWrapper.h

 // Copyright 2011, 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 254 matching lines @@
         // FIXME: the fact that we return 0 on error rather than asserting is
         // somewhat of a hack. We currently make this method return 0 because
         // we reuse this method to verify that objects are actually native
         // Node objects rather than objects that implement the Node interface.
         if (Dart_IsError(result))
             return 0;
         return reinterpret_cast<void*>(value);
     }
 
     template <class BindingsClass>
-    static void wrapperWeakCallback(Dart_WeakPersistentHandle, void* peer)
+    static void wrapperWeakCallback(Dart_WeakPersistentHandle wrapper, void* peer)
     {
         typedef DartDOMWrapperTraits<BindingsClass> Traits;
         DartDOMData* domData = DartDOMData::current();
         typename BindingsClass::NativeType* domObject = static_cast<typename BindingsClass::NativeType*>(peer);
+        Dart_WeakPersistentHandle currentWrapper = Traits::MapTraits::domMap(domData)->get(domObject);

[vsm, 2013/10/31 23:19:43]

Looking the IDB failures - if they are from this - you'll need a
DartIsolate/ApiScope:

../../dart/runtime/vm/handles_impl.h:99: error: expected:
isolate->no_handle_scope_depth() == 0

+        // This could be an old wrapper which has been replaced with a custom element.
+        if (currentWrapper != wrapper) {
+            ASSERT(!Dart_IdentityEquals(Dart_HandleFromWeakPersistent(currentWrapper), Dart_HandleFromWeakPersistent(wrapper)));
+            return;
+        }
+
         if (DartDOMWrapperTraits<BindingsClass>::MapTraits::domMap(domData)->contains(domObject)) {
             Traits::MapTraits::domMap(domData)->remove(domObject);
             Traits::ActiveTraits::removeWrapper(domData, domObject);
             Traits::EventTargetTraits::removeWrapper(domData, domObject);
         }
         domObject->deref();
     }
 
     template <class BindingsClass>
     static void associateWrapper(
@@ skipping 101 matching lines @@
         static DartMessagePortMap* domMap(DartDOMData* domData) { return domData->messagePortMap(); }
     };
     typedef MessagePortMapTraits MapTraits;
     typedef DartDOMWrapperActiveTraits<DartMessagePort, false> ActiveTraits;
     typedef DartDOMWrapperEventTargetTraits<DartMessagePort, true> EventTargetTraits;
 };
 
 }
 
 #endif // DartDOMWrapper_h