anchor.diff:  import 'package:build_integration/file_system/multi_root.dart';
   import 'package:compiler/src/kernel/dart2js_target.dart';
   import 'package:dev_compiler/src/kernel/target.dart';
  +import 'package:front_end/src/api_prototype/file_system.dart';
   import 'package:front_end/src/api_prototype/incremental_kernel_generator.dart';
   import 'package:front_end/src/api_unstable/bazel_worker.dart' as fe;
   import 'package:front_end/src/fasta/kernel/macro/macro.dart';
  
positive.code:   }
  }
  
  class DevCompilerSummaryTarget extends DevCompilerTarget with SummaryMixin {
    final List<Uri> sources;
    final bool excludeNonSources;
  
negative.code:   // system hides this from the front end.
    var multiRoots = parsedArgs['multi-root'].map(Uri.base.resolve).toList();
    if (multiRoots.isEmpty) multiRoots.add(Uri.base);
    MultiRootFileSystem mrfs = new MultiRootFileSystem(
        parsedArgs['multi-root-scheme'],
        multiRoots,
        fe.StandardFileSystem.instance);
    FileSystem fileSystem = mrfs;
    var sources = (parsedArgs['source'] as List<String>).map(toUri).toList();
    var excludeNonSources = parsedArgs['exclude-non-sources'] as bool;
  
  