anchor.diff:      ReceivePort port = new ReceivePort();
       initialReplyTo.send(port.sendPort);
       port.listen((request) async {
  -      if (request is _CacheCleanUpRequest) {
  +      if (request is CacheCleanUpRequest) {
           await _cleanUpFolder(request.cachePath, request.maxSizeBytes);
           // Let the client know that we're done.
           request.replyTo.send(true);
  
positive.code:       _evictionIsolateIsRunning = true;
        try {
          ReceivePort response = new ReceivePort();
          _cleanUpSendPort.send(new _CacheCleanUpRequest(
              _cachePath, _maxSizeBytes, response.sendPort));
          await response.first;
        } finally {
  
negative.code: 
  import 'package:analyzer/src/dart/analysis/byte_store.dart';
  import 'package:path/path.dart';
  
  /**
   * The request that is sent from the main isolate to the clean-up isolate.
   */
  class CacheCleanUpRequest {
    final String cachePath;
    final int maxSizeBytes;
    final SendPort replyTo;
  
    CacheCleanUpRequest(this.cachePath, this.maxSizeBytes, this.replyTo);
  }
  
  /**
   * [ByteStore] that stores values as files and performs cache eviction.
  