anchor.diff:  import 'package:bazel_worker/bazel_worker.dart';
   import 'package:front_end/src/api_unstable/summary_worker.dart' as fe;
   import 'package:front_end/src/multi_root_file_system.dart';
  +import 'package:kernel/ast.dart' show Program, Library;
   import 'package:kernel/target/targets.dart';
   
   main(List<String> args) async {
  
positive.code:     }
    }
  
    var sources = parsedArgs['source'].map(Uri.parse).toList();
    var summary = await fe.compile(state, sources, onProblem);
  
    if (summary != null) {
  
negative.code:   if (multiRoots.isEmpty) multiRoots.add(Uri.base);
    var fileSystem = new MultiRootFileSystem(parsedArgs['multi-root-scheme'],
        multiRoots, fe.PhysicalFileSystem.instance);
    var sources = parsedArgs['source'].map(Uri.parse).toList();
    var state = await fe.initializeCompiler(
        // TODO(sigmund): pass an old state once we can make use of it.
        null,
        Uri.base.resolve(parsedArgs['dart-sdk-summary']),
        Uri.base.resolve(parsedArgs['packages-file']),
        parsedArgs['input-summary'].map(Uri.base.resolve).toList(),
        new SummaryTarget(sources, parsedArgs['exclude-non-sources'],
            new TargetFlags(strongMode: true)),
        fileSystem);
  
    void onProblem(problem, severity, String formatted, line, column) {
  