DartProxy not deserialized as Dart object

When I get back a dart object that has been put in js code, I get an `Instance of 'Proxy'` instead of the local dart object. For instance the following test fails :

```dart
test('retrieve same dart Object', () {
  js.scoped(() {
    final date = new Date.now();
    js.context.dartDate = date;
    expect(js.context.dartDate, equals(date));
  });
});
```

I tried to dive into the code and fix that, but I did not succeed... The problem seems to be in :

```dart
deserializeObject(message) {
  var id = message[1];
  var port = message[2];
  if (port == _proxiedObjectTable.sendPort) {
    // Local object.
    return _proxiedObjectTable.get(id);
  } else {
    // Remote object.
    return new Proxy._internal(port, id);
  }
}
```

For the above test, `port` and `_proxiedObjectTable.sendPort` display `Instance of '_LocalSendPortSync@0x3918afae'` in debugger but `port == _proxiedObjectTable.sendPort` is evaluated as `false` and I don't know why.