er.
This behavior makes sure that no error is silently dropped.
However, it also means that error handlers should be installed early,
so that they are present as soon as a future is completed with an error.
The following example demonstrates this potential bug:</p>
<pre class="language-dart"><code>var future = getFuture();
new Timer(new Duration(milliseconds: 5), () {
  // The error-handler is not attached until 5 ms after the future has
  // been received. If the future fails before that, the error is
  //