<html>
<head>
<title>Blah</title>
</head>
<body>
This frame will fail to load with a DNS error.  "mock.failed.request" is the
magic hostname used by URLRequestFailedJob, and -105 is ERR_NAME_NOT_RESOLVED.
<iframe src="http://mock.failed.request/error?start=-105"></iframe>
</body>
</html>