title: How to use the schedule sampling in beam search decoder in tensorflow.
body: <p>The basic decoder contains a parameter to add helper method that can be a schedule sampling helper. But the beam search decoding does not contain any helper parameter. </p>
  
  <p>While in the code it looks like there is some sampling used, but it is not clear if schedule sampling is used or not.
  class BeamSearchDecoder(decoder.Decoder):
    """BeamSearch sampling decoder."""</p>
  
  <p>It would be nice to know and make my doubt clear.
  Would appreciate any light on this matter.
  Thanks in advance.</p>