Cancel client auth requests when not promptable.

chrome/test/data/extensions/api_test/xhr_fail/background.js

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+chrome.test.getConfig(function(config) {
+  var xhr = new XMLHttpRequest();
+  xhr.open("GET", config.customArg);
+  // The XHR is expected to fail.
+  xhr.onerror = function(ev) {
+    chrome.test.notifyPass();

[Ryan Sleevi, 2015/02/25 06:31:36]

If the test server breaks, this test will continue to succeed.

Is there anything we can do to isolate ourselves from this? Perhaps ensuring we
also make a successful connection to a known good testserver in the same test?
I'm not sure...

[davidben, 2015/02/26 18:09:41]

I was going to write why this is kind of a pain, and then I had a brilliant
idea! We could have the extension code watch its own request via
chrome.webRequest.

+  };
+  xhr.onload = function(ev) {
+    chrome.test.notifyFail("XHR unexpectedly passed");
+  };
+  xhr.send();
+});