Adding user into session doesn't generate login-prompt-visible.

chrome/browser/chromeos/login/login_display_host_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/login/login_display_host_impl.h"
 
 #include <vector>
 
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/desktop_background/user_wallpaper_delegate.h"
@@ skipping 391 matching lines @@
   return wizard_controller_.get();
 }
 
 void LoginDisplayHostImpl::StartUserAdding(
     const base::Closure& completion_callback) {
   restore_path_ = RESTORE_ADD_USER_INTO_SESSION;
   completion_callback_ = completion_callback;
   LOG(INFO) << "Login WebUI >> user adding";
   if (!login_window_)
     LoadURL(GURL(kUserAddingURL));
+  // We should emit this signal only at login screen (after reboot or sign out).
+  login_view_->set_should_emit_login_prompt_visible(false);
 
   // Lock container can be transparent after lock screen animation.
   aura::Window* lock_container = ash::Shell::GetContainer(
       ash::Shell::GetPrimaryRootWindow(),
       ash::internal::kShellWindowId_LockScreenContainersContainer);
   lock_container->layer()->SetOpacity(1.0);
 
   ash::Shell::GetInstance()->
       desktop_background_controller()->MoveDesktopToLockedContainer();
 
@@ skipping 535 matching lines @@
   VLOG(1) << "Initial time zone: " << timezone_name;
   // Apply locale customizations only once to preserve whatever locale
   // user has changed to during OOBE.
   if (!timezone_name.empty()) {
     chromeos::system::TimezoneSettings::GetInstance()->SetTimezoneFromID(
         UTF8ToUTF16(timezone_name));
   }
 }
 
 }  // namespace chromeos