anchor.diff:    For tree = parseStatement("for (int i = 0; i < 10; i = i + 1) { i = 5; }");
     visitor.visit(tree);
   
  -  BlockScope scope = visitor.scope;
  +  MethodScope scope = visitor.scope;
     Expect.equals(0, scope.elements.length);
     Expect.equals(10, map(visitor).length);
   
  
positive.code:   If tree = parseStatement("if (true) { var a = 1; a; } else { var a = 2; a;}");
    Element element = visitor.visit(tree);
    Expect.equals(null, element);
    BlockScope scope = visitor.scope;
    Expect.equals(0, scope.elements.length);
    Expect.equals(6, map(visitor).length);
  
  
negative.code:   Node tree = parseStatement("{ var a = 1; if (true) { a; } }");
    Element element = visitor.visit(tree);
    Expect.equals(null, element);
    MethodScope scope = visitor.scope;
    Expect.equals(0, scope.elements.length);
    Expect.equals(3, map(visitor).length);
    List<Element> elements = map(visitor).getValues();
  