Enable some profile_chrome unit tests on Trybots

systrace/profile_chrome/agents_unittest.py

 # Copyright 2014 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 time
 import unittest
 
 from profile_chrome import profiler
 
 from devil.android import device_utils
 from devil.android.sdk import intent
+from devil.android.sdk import keyevent
 
 
 class BaseAgentTest(unittest.TestCase):
   def setUp(self):
     devices = device_utils.DeviceUtils.HealthyDevices()
     self.browser = 'stable'
     self.package_info = profiler.GetSupportedBrowsers()[self.browser]
     self.device = devices[0]
 
+    # Turn on and unlock device in order to access the browser.
+    self.device.SetScreen(True)
+    self.device.SendKeyEvent(keyevent.KEYCODE_MENU)
+
     self.device.ForceStop(self.package_info.package)
     self.device.StartActivity(
         intent.Intent(activity=self.package_info.activity,
                       package=self.package_info.package),
         blocking=True)
+
+    # Sleep between unit tests to avoid race conditions.
+    time.sleep(5)

[Zhen Wang, 2016/09/01 23:16:56]

Have you figured out how to know if the browser is up running, so we can avoid
this sleep?

[Sami, 2016/09/02 13:01:13]

Yeah, it'd be great to avoid arbitrary sleeps since they might just make the
flake less likely but not completely eliminate it.

How does the test fail when we lose the race?

[washingtonp, 2016/09/08 22:51:36]

The chrome agent tests fail to find the start trace marker
and so the timeout for the method is reached.

By the way, I have moved this logic to a util function since
it is now also called within the chrome agent (since the chrome
agent requires the user to have the browser already open).

[washingtonp, 2016/09/08 22:51:36]

Unfortunately, from what I have repeatedly observed on my
device, the browser has to not only be open, but the page
has to finish loading as well. I have not been able to find
a way to check this, but I can add that as a TODO.