mash: Move SystemTrayDelegate ownership to WmShell

ash/system/web_notification/web_notification_tray_unittest.cc

Index: ash/system/web_notification/web_notification_tray_unittest.cc
diff --git a/ash/system/web_notification/web_notification_tray_unittest.cc b/ash/system/web_notification/web_notification_tray_unittest.cc
index 054c0d212ab8baf9f0ac7ffc7f5cfad74cea7261..ca3bcb6f3aea40c3d094015371bffa322c3ef7e0 100644
--- a/ash/system/web_notification/web_notification_tray_unittest.cc
+++ b/ash/system/web_notification/web_notification_tray_unittest.cc
@@ -288,7 +288,7 @@ TEST_F(WebNotificationTrayTest, MAYBE_PopupShownOnBothDisplays) {
   // Enables to appear the notification for display changes.
   test::TestSystemTrayDelegate* tray_delegate =

[msw, 2016/06/10 18:48:21]

nit: use AshTestBase::GetSystemTrayDelegate

[James Cook, 2016/06/10 20:20:32]

Done.

       static_cast<test::TestSystemTrayDelegate*>(
-          Shell::GetInstance()->system_tray_delegate());
+          WmShell::Get()->system_tray_delegate());
   tray_delegate->set_should_show_display_notification(true);
 
   UpdateDisplay("400x400,200x200");