anchor.diff:      }
   
       if (oldBuilt == null)
  -      _mountedComponents.add(this);
  +      _enqueueDidMount(this);
   
       int lastOrder = _currentOrder;
       _currentOrder = _order;
  
positive.code:     assert(oldNode == null || node._key == oldNode._key);
  
      if (node == oldNode) {
        _trace('_sync(identical) ${node._key}');
        return node; // Nothing to do. Subtrees must be identical.
      }
  
  
negative.code:     assert(_root != null);
      _removeChild(_built);
      _built = null;
      _enqueueDidUnmount(this);
      super._remove();
    }
  
  