anchor.diff:    }
   
     /// Update [this] using [map] as a source. [map] can be a reference.
  -  void update(Map map) {
  +  void updateFromServiceMap(Map map) {
       assert(_isServiceMap(map));
   
       // Don't allow the type to change on an object update.
  
positive.code:     if (obj == null) {
        obj = new ServiceMap._empty(owner);
      }
      obj.update(map);
      return obj;
    }
  
  
negative.code:     var type = _stripRef(map['type']);
      if (type == 'VM') {
        // Update this VM object.
        updateFromServiceMap(map);
        return this;
      }
  
  