anchor.diff:    }
   
     void _handlePackagesReply(msg) {
  -    assert(_packagesPort != null);
  +    if (_packagesPort == null) {
  +      return;
  +    }
       // Make sure to close the _packagePort before any other action.
       _packagesPort.close();
       _packagesPort = null;
  
positive.code:   RawReceivePort _packagesPort;
  
    void _requestPackagesMap([Uri packageConfig]) {
      assert(_packagesPort == null);
      assert(_rootScript != null);
      // Create a port to receive the packages map on.
      _packagesPort = new RawReceivePort(_handlePackagesReply);
      var sp = _packagesPort.sendPort;
  
negative.code:   IsolateLoaderState(this.isolateId);
  
    final int isolateId;
    bool _dead = false;
    SendPort sp;
  
    void init(String packageRootFlag, String packagesConfigFlag,
        String workingDirectory, String rootScript) {
      if (_dead) {
        return;
      }
      // _workingDirectory must be set first.
      _workingDirectory = new Uri.directory(workingDirectory);
      if (rootScript != null) {
  