anchor.diff:           num n;
            A a;
            B b;
  -         C c;
            y = a;
            o = a;
            i = /*severe:StaticTypeError*/a;
  
positive.code:          num n;
           A a;
           B b;
           C c;
           o = y;
           i = /*info:Unbox*/y;
           d = /*info:Unbox*/y;
           n = /*info:DownCast*/y;
           a = /*info:DownCast*/y;
           b = /*info:DownCast*/y;
           c = /*info:DownCast*/y;
        }
     '''
      });
  
negative.code: 
        class A {}
        class B extends A {}
  
        void main() {
           dynamic y;
  