anchor.diff:  
   import 'package:compiler/implementation/dart2jslib.dart' show
       Compiler,
  +    CompilerTask,
       Enqueuer,
       QueueFilter,
       WorkItem;
  
positive.code: modelx.ImportScope importScope(modelx.LibraryElementX element) {
    return element.importScope;
  }
  
negative.code:   LibraryUpdater updater =
        new LibraryUpdater(
            cachedCompiler, inputProvider, script, printWallClock, printVerbose);
    Future<bool> reuseLibrary(LibraryElement library) {
      return poiTask.measure(() => updater.reuseLibrary(library));
    }
  
    return reuseCompiler(
        diagnosticHandler: handler,
  