ReferenceError: DartObject is not defined
This is caused by the interop.js script not being included properly. It must be included as
<script src="packages/browser/interop.js"></script>and it must precede all other Dart related JavaScript includes. So the includes may for example look like this
<script src="packages/browser/interop.js"></script><script type="application/dart">export 'package:polymer/init.dart';</script><script src="packages/browser/dart.js"></script>In a Chrome Packaged App that uses the chrome package the includes may look like this
<script src="packages/browser/interop.js"></script><script src="packages/chrome/bootstrap.js" defer></script><script src="echo_mco.dart" type="application/dart"></script> The problem was being discussed and solved at https://code.google.com/p/dart/issues/detail?id=15065