anchor.diff:      var type = _stripRef(map['type']);
       if (type == 'VM') {
         // Update this VM object.
  -      update(map);
  +      updateFromServiceMap(map);
         return this;
       }
   
  
positive.code:   }
  
    /// Update [this] using [map] as a source. [map] can be a reference.
    void update(Map map) {
      assert(_isServiceMap(map));
  
      // Don't allow the type to change on an object update.
  
negative.code:   }
  
    VM() : super._empty(null) {
      updateFromServiceMap({'name': 'vm', 'type': '@VM'});
    }
  
    void postServiceEvent(String streamId, Map response, ByteData data) {
  