anchor.diff:  library my_lib1;
   import 'my_lib3.dart';
   ''');
  +    _expectInvalid(lib1Target);
  +    _expectInvalid(lib2Target);
  +    _expectInvalid(lib3Target);
  +
       // Ensure that invalidation correctly invalidated everything reachable
       // through lib3
       computeResult(lib1Target, LIBRARY_CYCLE);
  
positive.code:     computeResult(lib3Target, LIBRARY_CYCLE);
      expect(outputs[LIBRARY_CYCLE], hasLength(1));
  
      // complete the cycle
      context.setContents(
          lib1Source,
          '''
  library my_lib1;
  import 'my_lib3.dart';
  ''');
      computeResult(lib1Target, LIBRARY_CYCLE);
      expect(outputs[LIBRARY_CYCLE], hasLength(3));
      computeResult(lib2Target, LIBRARY_CYCLE);
  
negative.code:         '''
  library my_lib1;
  ''');
      _expectInvalid(lib1Target);
      _expectInvalid(lib2Target);
      _expectInvalid(lib3Target);
  
      computeResult(lib1Target, LIBRARY_CYCLE);
      expect(outputs[LIBRARY_CYCLE], hasLength(1));
      computeResult(lib2Target, LIBRARY_CYCLE);
  