Get a new copied object with only the directory path.

def Dirname(self):
    """Get a new copied object with only the directory path."""
    result = self.Copy()

    while 1:
      last_directory = posixpath.dirname(result.last.path)
      if last_directory != "/" or len(result) <= 1:
        result.last.path = last_directory
        # Make sure to clear the inode information.
        result.last.inode = None

        break

      result.Pop(-1)

    return result