anchor.diff:    useJs(new js.Blob(null));
     useJs(new js.NamedFunction(null, null));
     useJs(new js.ArrayHole());
  +  useJsBackend(null);
     useConcreteTypesInferrer(null);
     useColor();
     useFilenames();
  
positive.code:   node.asVariableUse();
  }
  
  useConcreteTypesInferrer(concrete_types_inferrer.ConcreteTypesInferrer c) {
    c.debug();
  }
  
negative.code: import 'inferrer/type_graph_inferrer.dart' as type_graph_inferrer;
  import 'io/code_output.dart' as io;
  import 'js/js.dart' as js;
  import 'js_backend/js_backend.dart' as js_backend;
  import 'js_emitter/js_emitter.dart' as js_emitter;
  import 'source_file_provider.dart' as source_file_provider;
  import 'ssa/ssa.dart' as ssa;
  