anchor.diff:  modelx.ImportScope importScope(modelx.LibraryElementX element) {
     return element.importScope;
   }
  +
  +class PoiTask extends CompilerTask {
  +  PoiTask(Compiler compiler) : super(compiler);
  +
  +  String get name => 'POI';
  +}
  
positive.code:       libraryRoot: libraryRoot,
        packageRoot: packageRoot,
        packagesAreImmutable: true,
        reuseLibrary: updater.reuseLibrary).then((Compiler newCompiler) {
      var filter = new ScriptOnlyFilter(script);
      newCompiler.enqueuerFilter = filter;
      return runPoiInternal(newCompiler, updater, position);
  
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,
  