Adds `tf.summary`s to all terms in the losses dictionary.

def _summarize_losses(self, losses_dict):
    """Adds `tf.summary`s to all terms in the losses dictionary."""
    if common_layers.should_generate_summaries():
      with tf.name_scope("losses"):
        for loss_name, loss_val in sorted(losses_dict.items()):
          tf.summary.scalar(loss_name, loss_val)