docs: def WriteBlobs(self, blob_id_data_map, cursor=None):
      """Writes given blobs."""
      chunks = []
      for blob_id, blob in iteritems(blob_id_data_map):
        chunks.extend(_BlobToChunks(blob_id.AsBytes(), blob))
      for values in _PartitionChunks(chunks):
        _Insert(cursor, "blobs", values)