anchor.diff:        _evictionIsolateIsRunning = true;
         try {
           ReceivePort response = new ReceivePort();
  -        _cleanUpSendPort.send(new _CacheCleanUpRequest(
  +        _cleanUpSendPort.send(new CacheCleanUpRequest(
               _cachePath, _maxSizeBytes, response.sendPort));
           await response.first;
         } finally {
  
positive.code:     return new File(join(_cachePath, key));
    }
  }
  
  /**
   * 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);
  }
  
negative.code:     ReceivePort port = new ReceivePort();
      initialReplyTo.send(port.sendPort);
      port.listen((request) async {
        if (request is CacheCleanUpRequest) {
          await _cleanUpFolder(request.cachePath, request.maxSizeBytes);
          // Let the client know that we're done.
          request.replyTo.send(true);
  