anchor.diff:  
     @override
     State rootAncestorStateOfType(TypeMatcher matcher) {
  -    assert(_debugCheckStateIsActiveForAncestorLoopkup());
  +    assert(_debugCheckStateIsActiveForAncestorLookup());
       Element ancestor = _parent;
       StatefulElement statefulAncestor;
       while (ancestor != null) {
  
positive.code: 
    @override
    State ancestorStateOfType(TypeMatcher matcher) {
      assert(_debugCheckStateIsActiveForAncestorLoopkup());
      Element ancestor = _parent;
      while (ancestor != null) {
        if (ancestor is StatefulElement && matcher.check(ancestor.state))
  
negative.code: 
    @override
    void visitAncestorElements(bool visitor(Element element)) {
      assert(_debugCheckStateIsActiveForAncestorLookup());
      Element ancestor = _parent;
      while (ancestor != null && visitor(ancestor))
        ancestor = ancestor._parent;
  