Callback refs: return the Dart component, not the JsObject instance
Callback refs: return the Dart component, not the JsObject instance

This behavior is in line with the `Component.ref`

evanweible-wf/react-dart,evanweible-wf/react-dart,cleandart/react-dart,cleandart/react-dart,cleandart/react-dart,evanweible-wf/react-dart,evanweible-wf/react-dart,cleandart/react-dart