Set window owner for Assistant opt-in dialog

Opt-in dialog should be hide/show correctly when switching users.

Bug: 812010
Test: Manual Test
Change-Id: I2a880974e22d1179c564891fc3f46f562de865f2
Reviewed-on: https://chromium-review.googlesource.com/c/1289685Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600972}

chrome/browser/ui/webui/chromeos/assistant_optin/assistant_optin_ui.cc

@@ -11,12 +11,14 @@
 #include "base/macros.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/browser/ui/ash/multi_user/multi_user_window_manager.h"
 #include "chrome/browser/ui/browser_dialogs.h"
 #include "chrome/browser/ui/webui/chromeos/login/base_screen_handler.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/browser_resources.h"
 #include "components/arc/arc_prefs.h"
 #include "components/prefs/pref_service.h"
+#include "components/user_manager/user_manager.h"
 #include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/web_ui.h"
 #include "content/public/browser/web_ui_data_source.h"
@@ -72,8 +74,12 @@ void AssistantOptInDialog::Show(
   int container_id = dialog->GetDialogModalType() == ui::MODAL_TYPE_NONE
                          ? ash::kShellWindowId_DefaultContainer
                          : ash::kShellWindowId_LockSystemModalContainer;
-  chrome::ShowWebDialogInContainer(
+  auto* window = chrome::ShowWebDialogInContainer(
       container_id, ProfileManager::GetActiveUserProfile(), dialog, true);
+
+  MultiUserWindowManager::GetInstance()->SetWindowOwner(
+      window,
+      user_manager::UserManager::Get()->GetActiveUser()->GetAccountId());
 }
 
 // static