anchor.diff:  }
   
   class StringMapWrapper {
  -  static HashMap create() => new HashMap();
  +  static Map create() => {};
     static bool contains(Map map, key) => map.containsKey(key);
     static get(Map map, key) => map[key];
     static void set(Map map, key, value) {
  
positive.code:   static void forEach(Map m, fn(v, k)) {
      m.forEach((k, v) => fn(v, k));
    }
    static HashMap merge(Map a, Map b) {
      var m = new HashMap.from(a);
      b.forEach((k, v) => m[k] = v);
      return m;
    }
  
negative.code: library facade.collection;
  
  import 'dart:collection' show IterableBase, Iterator;
  export 'dart:core' show Map, List, Set;
  import 'dart:math' show max, min;
  
  