Cancel client auth requests when not promptable.

chrome/test/data/extensions/background_xhr/test_http_auth.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.
+
+// TODO(davidben): When URLSearchParams is stable and implemented, switch this
+// (and a lot of other test code) to it. https://crbug.com/303152
+var url = decodeURIComponent(/url=([^&]*)/.exec(location.search)[1]);
+var filter = {urls: [url], types: ["xmlhttprequest"]};
+
+chrome.webRequest.onCompleted.addListener(function(details) {
+  chrome.test.assertEq(-1, details.tabId);
+  chrome.test.assertEq(url, details.url);
+  chrome.test.assertEq("xmlhttprequest", details.type);
+  chrome.test.assertEq(401, details.statusCode);
+
+  chrome.test.notifyPass();
+}, filter);
+
+chrome.webRequest.onErrorOccurred.addListener(function(details) {
+  chrome.test.notifyFail("Request failed");
+}, filter);
+
+chrome.runtime.sendMessage({type: "xhr", method: "GET", url: url});