def iter_chunks(self):
        """
        Generate a |_Chunk| subclass instance for each chunk in this parser's
        PNG stream, in the order encountered in the stream.
        """
        for chunk_type, offset in self._iter_chunk_offsets():
            chunk = _ChunkFactory(chunk_type, self._stream_rdr, offset)
            yield chunk
Generate a |_Chunk| subclass instance for each chunk in this parser's
        PNG stream, in the order encountered in the stream.