anchor.diff:  abstract class Completer<T> {
     factory Completer() => null;
     factory Completer.sync() => null;
  +
     Future<T> get future;
  +  bool get isCompleted;
  +
     void complete([value]);
     void completeError(Object error, [StackTrace stackTrace]);
  -  bool get isCompleted;
   }
   
   abstract class Timer {
  
positive.code:   _LIB_COLLECTION,
    _LIB_CONVERT,
    _LIB_FOREIGN_HELPER,
    _LIB_MATH,
    _LIB_HTML_DART2JS,
    _LIB_HTML_DARTIUM,
  
negative.code: import 'dart:async';
  
  abstract class Converter<S, T> implements StreamTransformer {}
  
  class JsonDecoder extends Converter<String, Object> {}
  ''',
      )
  