anchor.diff:  }
   
   class MapWrapper {
  -  static HashMap create() => new HashMap();
  -  static HashMap clone(Map m) => new HashMap.from(m);
  -  static HashMap createFromStringMap(Map m) => new Map.from(m);
  -  static HashMap createFromPairs(List pairs) => pairs.fold({}, (m, p) {
  +  static Map create() => {};
  +  static Map clone(Map m) => new Map.from(m);
  +  static Map createFromStringMap(Map m) => m;
  +  static Map createFromPairs(List pairs) => pairs.fold({}, (m, p) {
       m[p[0]] = p[1];
       return m;
     });
  
positive.code: library facade.collection;
  
  import 'dart:collection' show HashMap, IterableBase, Iterator;
  export 'dart:core' show Map, List, Set;
  import 'dart:math' show max, min;
  
  
negative.code:   static void forEach(Map m, fn(v, k)) {
      m.forEach((k, v) => fn(v, k));
    }
    static Map merge(Map a, Map b) {
      var m = new Map.from(a);
      b.forEach((k, v) => m[k] = v);
      return m;
    }
  