Use method that checks for autoupdate.

chrome/browser/chromeos/login/screen_locker.cc

Index: chrome/browser/chromeos/login/screen_locker.cc
diff --git a/chrome/browser/chromeos/login/screen_locker.cc b/chrome/browser/chromeos/login/screen_locker.cc
index e889aa3b9c67128d4e0591b5baa4b5a61404b88e..1ed42df8046785a30e9ab3e06596db1f05325aad 100644
--- a/chrome/browser/chromeos/login/screen_locker.cc
+++ b/chrome/browser/chromeos/login/screen_locker.cc
@@ -25,6 +25,7 @@
 #include "chrome/browser/chromeos/login/login_utils.h"
 #include "chrome/browser/chromeos/login/user_manager.h"
 #include "chrome/browser/chromeos/login/webui_screen_locker.h"
+#include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/signin/signin_manager.h"
@@ -288,7 +289,9 @@ void ScreenLocker::EnableInput() {
 void ScreenLocker::Signout() {

[Nikita (slow), 2013/04/08 17:05:53]

It seem that there're autotests that employ this functionality.

I've executed cros_* trybots to check it.

   delegate_->ClearErrors();
   content::RecordAction(UserMetricsAction("ScreenLocker_Signout"));
-  DBusThreadManager::Get()->GetSessionManagerClient()->StopSession();
+  // We expect that this call will not wait for any user input.
+  // If it changes at some point, we will need to force exit.
+  chrome::AttemptUserExit();
 
   // Don't hide yet the locker because the chrome screen may become visible
   // briefly.