Fix flakiness in pyauto test on ChromeOS: ntp.NTPTest.testThumbnailPersistence.

chrome/test/pyautolib/pyauto.py

 #!/usr/bin/python
 
 # Copyright (c) 2011 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.
 
 """PyAuto: Python Interface to Chromium's Automation Proxy.
 
 PyAuto uses swig to expose Automation Proxy interfaces to Python.
 For complete documentation on the functionality available,
@@ skipping 153 matching lines @@
       self.UseNamedChannelID(named_channel_id)
     self.SetUp()     # Fire browser
 
     # TODO(dtu): Remove this after crosbug.com/4558 is fixed.
     if self.IsChromeOS():
       self.WaitUntil(lambda: not self.GetNetworkInfo()['offline_mode'])
 
   def tearDown(self):
     self.TearDown()  # Destroy browser
 
-  @staticmethod
-  def CloseChromeOnChromeOS():
+  def CloseChromeOnChromeOS(self):
     """Gracefully exit chrome on ChromeOS."""
+
+    def _GetListOfChromePids():
+      """Retrieves the list of currently-running Chrome process IDs.
+
+      Returns:
+        A list of strings, where each string represents a currently-running
+        'chrome' process ID.
+      """
+      proc = subprocess.Popen(['pgrep', 'chrome'], stdout=subprocess.PIPE)
+      proc.wait()
+      return [x.strip() for x in proc.stdout.readlines()]
+
+    orig_pids = _GetListOfChromePids()
     subprocess.call(['pkill', 'chrome'])
 
+    def _AreOrigPidsDead(orig_pids):
+      """Determines whether all originally-running 'chrome' processes are dead.
+
+      Args:
+        orig_pids: A list of strings, where each string represents the PID for
+                   an originally-running 'chrome' process.
+
+      Returns:
+        True, if all originally-running 'chrome' processes have been killed, or
+        False otherwise.
+      """
+      for new_pid in _GetListOfChromePids():
+        if new_pid in orig_pids:
+          return False
+      return True
+
+    self.WaitUntil(lambda: _AreOrigPidsDead(orig_pids))
+
   def EnableChromeTestingOnChromeOS(self):
     """Enables the named automation interface on chromeos.
 
     Restarts chrome so that you get a fresh instance.
     Also sets some testing-friendly flags for chrome.
 
     Expects suid python to be present in the same dir as pyautolib.py
     """
     def _IsRootSuid(path):
       return os.path.isfile(path) and (os.stat(path).st_mode & stat.S_ISUID)
@@ skipping 3435 matching lines @@
     if self._options.verbose:
       verbosity = 2
     result = PyAutoTextTestRuner(verbosity=verbosity).run(pyauto_suite)
     del loaded_tests  # Need to destroy test cases before the suite
     del pyauto_suite
     sys.exit(not result.wasSuccessful())
 
 
 if __name__ == '__main__':
   Main()