anchor.diff:  import 'dart:async';
   
   class Object {
  -  const Object() {}
  +  const Object();
     bool operator ==(other) => identical(this, other);
     String toString() => 'a string';
     int get hashCode => 0;
  
positive.code:   Iterable/*<R>*/ map/*<R>*/(/*=R*/ f(E e));
  
    /*=R*/ fold/*<R>*/(/*=R*/ initialValue,
        /*=R*/ combine(/*=R*/ previousValue, E element));
  
    Iterable/*<T>*/ expand/*<T>*/(Iterable/*<T>*/ f(E element));
  
  
negative.code:   int get length;
    Iterable<V> get values;
  }
  
  class Duration implements Comparable<Duration> {}
  
  external bool identical(Object a, Object b);
  
  