[chromeos] Fix Logout automation when no browser windows are present.

chrome/test/pyautolib/pyauto.py

Index: chrome/test/pyautolib/pyauto.py
diff --git a/chrome/test/pyautolib/pyauto.py b/chrome/test/pyautolib/pyauto.py
index ce70de14a6c0c24ca2b1dbee9ee73e06f290a237..c04b30424020176d228a22e69bc4f66978ac0364 100755
--- a/chrome/test/pyautolib/pyauto.py
+++ b/chrome/test/pyautolib/pyauto.py
@@ -4117,14 +4117,18 @@ class PyUITest(pyautolib.PyUITestBase, unittest.TestCase):
   def Logout(self):
     """Log out from ChromeOS and wait for session_manager to come up.
 
-    May return before logout is complete and
-    gives no indication of success or failure.
-    Should be logged in to work.
+    This is equivalent to pressing the 'Sign out' button from the
+    aura shell tray when logged in.
+
+    Should be logged in to work. Re-initializes the automation channel
+    after logout.
     """
     assert self.GetLoginInfo()['is_logged_in'], \
         'Trying to log out when already logged out.'
-    assert self.WaitForSessionManagerRestart(
-        lambda: self.ApplyAccelerator(IDC_EXIT)), \
+    def _SignOut():
+      cmd_dict = { 'command': 'SignOut' }
+      self._GetResultFromJSONRequest(cmd_dict, windex=None)
+    assert self.WaitForSessionManagerRestart(_SignOut), \
         'Session manager did not restart after logout.'
     self.__SetUp()