d will stay subscribed until this stream ends,
or a callback cancels the subscription.</p>
<p>If <code>onListen</code> is provided, it is called with a subscription-like object
that represents the underlying subscription to this stream. It is
possible to pause, resume or cancel the subscription during the call
to <code>onListen</code>. It is not possible to change the event handlers, including
using <a href="dart-async/StreamSubscription/asFuture.html">StreamSubscription.asFuture</a>.</p>
<p>If <code>onCanc