[Telemetry] fix run_benchmark crash on CrOS

telemetry/telemetry/internal/backends/chrome/cros_browser_backend.py

 # Copyright 2013 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 logging
 import os
 
 from telemetry.core import exceptions
 from telemetry.core import util
 from telemetry import decorators
@@ skipping 149 matching lines @@
             '--dest=org.chromium.SessionManager',
             '/org/chromium/SessionManager',
             'org.chromium.SessionManagerInterface.EnableChromeTesting',
             'boolean:true',
             'array:string:"%s"' % ','.join(startup_args)]
     logging.info(' '.join(args))
     self._cri.RunCmdOnDevice(args)
 
     # Wait for new chrome and oobe.
     py_utils.WaitFor(lambda: pid != self.pid, 15)
-    self._WaitForBrowserToComeUp()
+    # Disable tracing for the login-screen instance of Chrome, otherwise
+    # tracing on the instance of Chrome running the benchmark will fail.
+    self._WaitForBrowserToComeUp(enable_tracing=False)
     py_utils.WaitFor(lambda: self.oobe_exists, 30)
 
     if self.browser_options.auto_login:
       if self._is_guest:
         pid = self.pid
         self.oobe.NavigateGuestLogin()
         # Guest browsing shuts down the current browser and launches an
         # incognito browser in a separate process, which we need to wait for.
         try:
           # TODO(achuith): Reduce this timeout to 15 sec after crbug.com/631640
           # is resolved.
           py_utils.WaitFor(lambda: pid != self.pid, 60)
         except py_utils.TimeoutException:
           self._RaiseOnLoginFailure(
               'Failed to restart browser in guest mode (pid %d).' % pid)
 
       elif self.browser_options.gaia_login:
         self.oobe.NavigateGaiaLogin(self._username, self._password)
       else:
         self.oobe.NavigateFakeLogin(
             self._username, self._password, self._gaia_id,
             not self.browser_options.disable_gaia_services)
 
       try:
-        self._WaitForLogin()
+        self._WaitForLogin(enable_tracing=True)
       except py_utils.TimeoutException:
         self._RaiseOnLoginFailure('Timed out going through login screen. '
                                   + self._GetLoginStatus())
 
     logging.info('Browser is up!')
 
   def Background(self):
     raise NotImplementedError
 
   def Close(self):
@@ skipping 77 matching lines @@
       status += 'Browser didn\'t launch. '
     if self.oobe_exists:
       status += 'OOBE not dismissed.'
     return status
 
   def _IsLoggedIn(self):
     """Returns True if cryptohome has mounted, the browser is
     responsive to devtools requests, and the oobe has been dismissed."""
     return not self._GetLoginStatus()
 
-  def _WaitForLogin(self):
+  def _WaitForLogin(self, enable_tracing):
     # Wait for cryptohome to mount.
     py_utils.WaitFor(self._IsLoggedIn, 900)
 
     # For incognito mode, the session manager actually relaunches chrome with
     # new arguments, so we have to wait for the browser to come up.
-    self._WaitForBrowserToComeUp()
+    self._WaitForBrowserToComeUp(enable_tracing)

[achuithb, 2017/08/17 15:29:26]

I think we may be able to get rid of this call, but maybe try that in a
follow-up CL.

 
     # Wait for extensions to load.
     if self._supports_extensions:
       self._WaitForExtensionsToLoad()
 
   def _RaiseOnLoginFailure(self, error):
     if self._platform_backend.CanTakeScreenshot():
       self._cri.TakeScreenshotWithPrefix('login-screen')
     raise exceptions.LoginException(error)