cros: Disable system tray help/lock buttons during supervised user creation

ash/test/test_session_controller_client.h

Index: ash/test/test_session_controller_client.h
diff --git a/ash/test/test_session_controller_client.h b/ash/test/test_session_controller_client.h
index 0163bb2ef14f8d4a4501f1fe930d8c4ba6fa1b89..6524a9e77fa616016e8d3f575d1626b9dee8b0bb 100644
--- a/ash/test/test_session_controller_client.h
+++ b/ash/test/test_session_controller_client.h
@@ -50,8 +50,10 @@ class TestSessionControllerClient : public ash::mojom::SessionControllerClient {
   void CreatePredefinedUserSessions(int count);
 
   // Adds a user session from a given display email. The display email will be
-  // canonicalized and used to construct an AccountId.
-  void AddUserSession(const std::string& display_email);
+  // canonicalized and used to construct an AccountId. |enable_settings| sets
+  // whether web UI settings are allowed.
+  void AddUserSession(const std::string& display_email,
+                      bool enable_settings = true);
 
   // Simulates screen unlocking. It is virtual so that test cases can override
   // it. The default implementation sets the session state of SessionController