message: Update tpu_embedding.py to reduce the number of constant tensors it creates.
diff: @@ -1139,6 +1139,8 @@ class TPUEmbedding(object):
  'table_ids': [],
  'max_sequence_lengths': [],
  }
  + int_zeros = array_ops.zeros((0,), dtype=dtypes.int64)
  + float_zeros = array_ops.zeros((0,), dtype=dtypes.float32)
  for table_id, table in enumerate(self._table_to_features_dict):
  features = self._table_to_features_dict[table]
  for feature in features:
  @@ -1146,13 +1148,11 @@ class TPUEmbedding(object):
  kwargs['sample_indices'].append(
  enqueue_data.sample_indices
  - if enqueue_data.sample_indices is not None else array_ops.zeros(
  - (0,), dtype=dtypes.int64))
  + if enqueue_data.sample_indices is not None else int_zeros)
  kwargs['aggregation_weights'].append(
  enqueue_data.aggregation_weights if
  - enqueue_data.aggregation_weights is not None else array_ops.zeros(
  - (0,), dtype=dtypes.float32))
  + enqueue_data.aggregation_weights is not None else float_zeros)
  kwargs['embedding_indices'].append(enqueue_data.embedding_indices)
  