anchor.diff:  String dirname(String path) {
     int index = path.lastIndexOf('/');
     return index == -1 ? '' : path.substring(0, index);
  +}
  +
  +String pathconcat(String path1, String path2) {
  +  if (path1.isEmpty) {
  +    return path2;
  +  }
  +  if (path2.isEmpty){
  +    return path1;
  +  }
  +  if (path1.endsWith("/") || path2.startsWith("/")) {
  +    return path1 + path2;
  +  }
  +  return path1 + "/" + path2;
   }
   
   /**
  
positive.code:       throw new UnsupportedError("StringSource doesn't support uriKind.");
  
    @override
    Uri get uri => new Uri.file(fullName);
  
    @override
    int get hashCode => _contents.hashCode ^ fullName.hashCode;
  
negative.code:       return null;
      }
  
      // TODO(rpaquay): This is somewhat brittle, as this relies on the specific
      // format of [uuid] returned by the Workspace implementation.
      // Example:
      //   context.id = "chrome-app-id:application-name"
      //   uri.path = "path-to-source-file-within-chrome-app"
      String uuid = pathconcat(context.id, uri.path);
      return context.getSource(uuid);
    }
  }
  
  