code: func ackPublishMetricHandler(timer *time.Timer) func(*ecstcs.AckPublishMetric) {
  	return func(*ecstcs.AckPublishMetric) {
  		seelog.Debug("Received AckPublishMetric from tcs")
  		timer.Reset(retry.AddJitter(defaultHeartbeatTimeout, defaultHeartbeatJitter))
  	}
  }
docs: // ackPublishMetricHandler consumes the ack message from the backend. THe backend sends
  // the ack each time it processes a metric message.