Add integration test for disabled bypass on missing via header

Also makes a small change to the GetWarmupURL() function in order to
allow this testing to work by preserving existing query params.

Cleans up a bit of whitespace in bypass.py

Bug: 724704
Change-Id: Ia84d1199911725684c00538f9ef651a427a9d279
Reviewed-on: https://chromium-review.googlesource.com/1024727
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553187}

tools/chrome_proxy/webdriver/bypass.py

@@ -5,6 +5,7 @@
 import common
 from common import TestDriver
 from common import IntegrationTest
+from decorators import ChromeVersionEqualOrAfterM
 
 
 class Bypass(IntegrationTest):
@@ -102,6 +103,47 @@ class Bypass(IntegrationTest):
       for response in responses:
         self.assertHasChromeProxyViaHeader(response)
 
+  # Verify that Chrome does not bypass the proxy when a response gets a missing
+  # via header.
+  @ChromeVersionEqualOrAfterM(67)
+  def testMissingViaHeaderNoBypassExperiment(self):
+    with TestDriver() as t:
+      t.AddChromeArg('--enable-spdy-proxy-auth')
+      t.AddChromeArg('--enable-features=DataReductionProxyRobustConnection'
+        '<DataReductionProxyRobustConnection')
+      t.AddChromeArg('--force-fieldtrials=DataReductionProxyRobustConnection/'
+        'Enabled')
+      t.AddChromeArg('--force-fieldtrial-params='
+        'DataReductionProxyRobustConnection.Enabled:'
+        'warmup_fetch_callback_enabled/true/'
+        'bypass_missing_via_disabled/true')
+      t.AddChromeArg('--disable-data-reduction-proxy-warmup-url-fetch')
+      t.AddChromeArg('--data-reduction-proxy-http-proxies='
+        # The chromeproxy-test server is a simple HTTP server. If it is served a
+        # proxy-request, it will respond with a 404 error page. It will not set
+        # the Via header on the response.
+        'https://chromeproxy-test.appspot.com;http://compress.googlezip.net')
+
+      # Loading this URL should not hit the actual check.googlezip.net origin.
+      # Instead, the test server proxy should fully handle the request and will
+      # respond with an error page.
+      t.LoadURL("http://check.googlezip.net/test.html")
+      for response in t.GetHTTPResponses():
+        self.assertNotHasChromeProxyViaHeader(response)
+
+      # Check the via bypass histograms are empty.
+      histogram = t.GetHistogram(
+        'DataReductionProxy.BypassedBytes.MissingViaHeader4xx')
+      self.assertEqual(0, len(histogram))
+      histogram = t.GetHistogram(
+        'DataReductionProxy.BypassedBytes.MissingViaHeaderOther')
+      self.assertEqual(0, len(histogram))
+
+      # Check that the fetch used the proxy.
+      histogram = t.GetHistogram('DataReductionProxy.ProxySchemeUsed')
+      self.assertEqual(histogram['buckets'][0]['low'], 2)
+      self.assertEqual(histogram['buckets'][0]['high'], 3)
+
   # Verify that when Chrome receives a 4xx response through a Data Reduction
   # Proxy that doesn't set a proper via header, Chrome bypasses all proxies and
   # retries the request over direct.