anchor.diff:    /**
      * Construct a new Firebase reference from a full Firebase URL.
      */
  -  Firebase(String url) {
  -    this._fb = new JsObject(context['Firebase'], [url]);
  -  }
  +  Firebase(String url) : super(url);
   
     /**
      * Construct a new Firebase reference from a JsObject.
      */
  -  Firebase.fromJsObject(JsObject obj) {
  -    this._fb = obj;
  -  }
  +  Firebase.fromJsObject(JsObject obj) : super.fromJsObject(obj);
   
     /**
      * Authenticates a Firebase client using a provided Authentication token.
  
positive.code: import 'dart:async';
  import 'dart:convert';
  
  class Firebase {
    JsObject _fb;
  
    /**
     * Resolve a future, given an error and result.
     */
  
negative.code:      return c.future;
     }
  }
  