Unflake some tests

Also skip lofi fallback test in M74, that fails due to server support
removed.

Bug: 934875
Change-Id: Ic5d0d00d63d95cf458e0afc3eaf0a3cf16743c01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611078
Reviewed-by: Robert Ogden <robertogden@chromium.org>
Commit-Queue: rajendrant <rajendrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659254}

tools/chrome_proxy/webdriver/lite_page.py

@@ -135,6 +135,8 @@ def testStaleLitePageNano(self):
       test_driver.LoadURL(
         'http://check.googlezip.net/cacheable/test.html?age_seconds=360')
 
+      test_driver.SleepUntilHistogramHasEntry(
+        'Previews.StalePreviewTimestampShown')
       histogram = test_driver.GetBrowserHistogram(
         'Previews.StalePreviewTimestampShown')
       self.assertEqual(1, histogram['count'])
@@ -158,7 +160,7 @@ def testStaleLitePageNano(self):
   # Verifies Lo-Fi fallback via the page-policies server directive.
   # Note: this test is for the CPAT protocol change in M-61.
   @ChromeVersionEqualOrAfterM(61)
-  @ChromeVersionBeforeM(75)
+  @ChromeVersionBeforeM(74)
   def testLitePageFallbackViaPagePolicies(self):
     with TestDriver() as test_driver:
       test_driver.AddChromeArg('--enable-spdy-proxy-auth')

tools/chrome_proxy/webdriver/smoke.py

@@ -78,6 +78,7 @@ def testPingback(self):
       t.LoadURL('http://check.googlezip.net/test.html')
       t.LoadURL('http://check.googlezip.net/test.html')
       t.SleepUntilHistogramHasEntry("DataReductionProxy.Pingback.Succeeded")
+      t.SleepUntilHistogramHasEntry("DataReductionProxy.Pingback.Attempted")
       # Verify one pingback attempt that was successful.
       attempted = t.GetBrowserHistogram('DataReductionProxy.Pingback.Attempted')
       self.assertEqual(1, attempted['count'])