Adding a probe fallback to HTTP test

tools/chrome_proxy/webdriver/fallback.py

+# Copyright 2017 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.
+
+import common
+from common import TestDriver
+from common import IntegrationTest
+
+class Fallback(IntegrationTest):
+
+  # Ensure that when a carrier blocks using the secure proxy, requests fallback
+  # to the HTTP proxy server.
+  def testSecureProxyProbeFallback(self):
+    with TestDriver() as test_driver:
+      test_driver.AddChromeArg('--enable-spdy-proxy-auth')
+
+      # Set the secure proxy check URL to the google.com favicon, which will be
+      # interpreted as a secure proxy check failure since the response body is
+      # not "OK". The google.com favicon is used because it will load reliably
+      # fast, and there have been problems with chromeproxy-test.appspot.com
+      # being slow and causing tests to flake.
+      test_driver.AddChromeArg(
+          '--data-reduction-proxy-secure-proxy-check-url='
+          'http://www.google.com/favicon.ico')
+
+      # Start chrome to begin the secure proxy check
+      test_driver.LoadURL('http://www.google.com/favicon.ico')
+
+      self.assertTrue(
+        test_driver.SleepUntilHistogramHasEntry("DataReductionProxy.ProbeURL"))
+
+      test_driver.LoadURL('http://check.googlezip.net/test.html')
+      responses = test_driver.GetHTTPResponses()
+      self.assertNotEqual(0, len(responses))
+      for response in responses:
+          self.assertHasChromeProxyViaHeader(response)
+          self.assertEqual(u'http/1.1', response.protocol)
+
+if __name__ == '__main__':
+  IntegrationTest.RunAllTests()