Add additional logging to diagnose flaky testZipInIncognito test

functional/downloads.py

 #!/usr/bin/python
 # Copyright (c) 2010 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 commands
 import filecmp
 import logging
 import os
 import shutil
@@ skipping 134 matching lines @@
     downloaded_pkg = os.path.join(self.GetDownloadDirectory().value(),
                                   'a_zip_file.zip')
     self._ClearLocalDownloadState(downloaded_pkg)
 
     self.RunCommand(pyauto.IDC_NEW_INCOGNITO_WINDOW)  # open incognito window
     # Downloads from incognito window do not figure in GetDownloadsInfo()
     # since the download manager's list doesn't contain it.
     # Using WaitUntil is the only resort.
     self.NavigateToURL(file_url, 1, 0)
     self.assertTrue(self.WaitUntil(lambda: os.path.exists(downloaded_pkg)))
-    self.assertTrue(self._EqualFileContents(file_path, downloaded_pkg))
+    self.assertTrue(self._EqualFileContents(file_path, downloaded_pkg),
+        msg='%s (size %d) and %s (size %d) do not match' % (
+            file_path, os.path.getsize(file_path),
+            downloaded_pkg, os.path.getsize(downloaded_pkg)))
     self.assertTrue(self.IsDownloadShelfVisible(1))
 
   def testSaveDangerousFile(self):
     """Verify that we can download and save a dangerous file."""
     file_path = self._GetDangerousDownload()
     downloaded_pkg = os.path.join(self.GetDownloadDirectory().value(),
                                   os.path.basename(file_path))
     self._ClearLocalDownloadState(downloaded_pkg)
     self._TriggerUnsafeDownload(os.path.basename(file_path))
     self.PerformActionOnDownload(self._GetDownloadId(),
@@ skipping 429 matching lines @@
 
     # Verify download in Incognito Window.
     # WaitForAllDownloadsToComplete does not wait for incognito downloads
     self.assertTrue(self.WaitUntil(
         lambda: os.path.exists(downloaded_pkg_incog)))
     self.assertTrue(self._EqualFileContents(file_path, downloaded_pkg_incog))
 
 
 if __name__ == '__main__':
   pyauto_functional.Main()