Writes file chunk.

def WriteFileChunk(self, chunk):
    """Writes file chunk."""
    precondition.AssertType(chunk, bytes)

    if not self._stream:
      raise ArchiveAlreadyClosedError(
          "Attempting to write to a ZIP archive that was already closed.")

    self.cur_file_size += len(chunk)
    # TODO(user):pytype: crc32 is not visible outside of zipfile.
    # pytype: disable=module-attr
    self.cur_crc = zipfile.crc32(chunk, self.cur_crc) & 0xffffffff
    # pytype: enable=module-attr

    if self.cur_cmpr:
      chunk = self.cur_cmpr.compress(chunk)
      self.cur_compress_size += len(chunk)

    self._stream.write(chunk)
    return self._stream.GetValueAndReset()