cros: Various fixes needed for preloading lock screen.

chrome/browser/chromeos/login/ui/user_adding_screen_browsertest.cc

Index: chrome/browser/chromeos/login/ui/user_adding_screen_browsertest.cc
diff --git a/chrome/browser/chromeos/login/ui/user_adding_screen_browsertest.cc b/chrome/browser/chromeos/login/ui/user_adding_screen_browsertest.cc
index 038a6e9f8437ed42182e623ce03d4a514c3438d5..2cd6df2ec88bddc4024fb9f530743ae29dc4fad7 100644
--- a/chrome/browser/chromeos/login/ui/user_adding_screen_browsertest.cc
+++ b/chrome/browser/chromeos/login/ui/user_adding_screen_browsertest.cc
@@ -266,15 +266,21 @@ IN_PROC_BROWSER_TEST_F(UserAddingScreenTest, ScreenVisibility) {
   WaitUntilUserAddingFinishedOrCancelled();
   content::RunAllPendingInMessageLoop();
 
-  ScreenLocker::Show();
-  content::WindowedNotificationObserver(
-      chrome::NOTIFICATION_SCREEN_LOCK_STATE_CHANGED,
-      content::NotificationService::AllSources()).Wait();
-
-  ScreenLocker::Hide();
-  content::WindowedNotificationObserver(
-      chrome::NOTIFICATION_SCREEN_LOCK_STATE_CHANGED,
-      content::NotificationService::AllSources()).Wait();
+  {
+    content::WindowedNotificationObserver observer(
+        chrome::NOTIFICATION_SCREEN_LOCK_STATE_CHANGED,
+        content::NotificationService::AllSources());
+    ScreenLocker::Show();
+    observer.Wait();
+  }
+
+  {
+    content::WindowedNotificationObserver observer(
+        chrome::NOTIFICATION_SCREEN_LOCK_STATE_CHANGED,
+        content::NotificationService::AllSources());
+    ScreenLocker::Hide();
+    observer.Wait();
+  }
 
   UserAddingScreen::Get()->Start();
   content::RunAllPendingInMessageLoop();