Switch WindowedNotificationObserver to use base::RunLoop.

chrome/browser/chromeos/login/login_manager_test.cc

Index: chrome/browser/chromeos/login/login_manager_test.cc
diff --git a/chrome/browser/chromeos/login/login_manager_test.cc b/chrome/browser/chromeos/login/login_manager_test.cc
index 354f2dc318f4475264c2bbdabcda73a3c1231611..5e9bcdb54b0f105ac89f227df43cde1534d2824a 100644
--- a/chrome/browser/chromeos/login/login_manager_test.cc
+++ b/chrome/browser/chromeos/login/login_manager_test.cc
@@ -201,6 +201,8 @@ void LoginManagerTest::LoginUser(const std::string& user_id) {
   const UserContext user_context = CreateUserContext(user_id);
   SetExpectedCredentials(user_context);
   EXPECT_TRUE(TryToLogin(user_context));
+  // Let LoginDisplayHostImpl delete itself.
+  content::RunAllPendingInMessageLoop();
 }
 
 void LoginManagerTest::AddUser(const std::string& user_id) {