anchor.diff:  import 'package:crypto/crypto.dart';
   import 'package:front_end/src/base/api_signature.dart';
   import 'package:front_end/src/base/performace_logger.dart';
  +import 'package:front_end/src/byte_store/byte_store.dart';
   import 'package:front_end/src/fasta/builder/builder.dart' as fasta;
   import 'package:front_end/src/fasta/parser/parser.dart' as fasta;
   import 'package:front_end/src/fasta/scanner.dart' as fasta;
  -import 'package:front_end/src/byte_store/byte_store.dart';
   import 'package:meta/meta.dart';
   
   /**
  
positive.code:   }
  
    void _scheduleKnownFilesSetChange() {
      Duration delay = _knownFilesSetChangesDelay ?? new Duration(seconds: 1);
      _knownFilesSetChangesTimer ??= new Timer(delay, () {
        Set<String> addedFiles = _addedKnownFiles.toSet();
  
negative.code:    * Return the [Stream] that is periodically notified about changes to the
     * known files set.
     */
    Stream<KnownFilesSetChange> get knownFilesSetChanges {
      // If this is the first (and actually the only) time when the stream is
      // requested, schedule the timer to send updates.
      if (!_knownFilesSetChangesRequested) {
        _knownFilesSetChangesRequested = true;
        _scheduleKnownFilesSetChange();
      }
      return _knownFilesSetChangesController.stream;
    }
  
    @visibleForTesting
    FileSystemStateTestView get test => _testView;
  