function timeoutPromise(t, ms) {
  return new Promise(resolve => { t.step_timeout(resolve, ms); });
}
@typedef SourceContext
  @type {object}

  @property {string} sourceContextType
    Kind of the source context to be used.
    Valid values are the keys of `sourceContextMap` below.

  @property {Array<PolicyDelivery>} policyDeliveries
    A list of PolicyDelivery applied to the source context.