Migrate user adding screen to view-based implementation

Bug: 1066489
Change-Id: Ic997e1b8de256ab66ef28710ff41c2ff9299a378
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2219889
Commit-Queue: Thomas Tellier <tellier@google.com>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784827}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index 552c522..a3d1851 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -399,11 +399,12 @@
 
 void LoginScreenController::ShowLoginScreen() {
   // Login screen can only be used during login.
-  CHECK_EQ(session_manager::SessionState::LOGIN_PRIMARY,
-           Shell::Get()->session_controller()->GetSessionState())
+  session_manager::SessionState session_state =
+      Shell::Get()->session_controller()->GetSessionState();
+  CHECK(session_state == session_manager::SessionState::LOGIN_PRIMARY ||
+        session_state == session_manager::SessionState::LOGIN_SECONDARY)
       << "Not showing login screen since session state is "
-      << static_cast<int>(
-             Shell::Get()->session_controller()->GetSessionState());
+      << static_cast<int>(session_state);
 
   OnShow();
   // TODO(jdufault): rename LockScreen to LoginScreen.