mash: Move SystemTrayDelegate ownership to WmShell

ash/system/chromeos/supervised/tray_supervised_user_unittest.cc

Index: ash/system/chromeos/supervised/tray_supervised_user_unittest.cc
diff --git a/ash/system/chromeos/supervised/tray_supervised_user_unittest.cc b/ash/system/chromeos/supervised/tray_supervised_user_unittest.cc
index 5ff429555d82fda993242eb0a31b3a74ba7fda89..d3191075035aa112a961279c37ed1299d6fe4ed3 100644
--- a/ash/system/chromeos/supervised/tray_supervised_user_unittest.cc
+++ b/ash/system/chromeos/supervised/tray_supervised_user_unittest.cc
@@ -4,7 +4,7 @@
 
 #include "ash/system/chromeos/supervised/tray_supervised_user.h"
 
-#include "ash/shell.h"
+#include "ash/common/wm_shell.h"
 #include "ash/system/user/login_status.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/test/test_system_tray_delegate.h"
@@ -65,7 +65,7 @@ void TraySupervisedUserInitialTest::TearDown() {
 TEST_F(TraySupervisedUserTest, SupervisedUserHasNotification) {
   test::TestSystemTrayDelegate* delegate =

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

nit: use AshTestBase::GetSystemTrayDelegate

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

Done. (I'm glad you noticed these!)

       static_cast<test::TestSystemTrayDelegate*>(
-          ash::Shell::GetInstance()->system_tray_delegate());
+          WmShell::Get()->system_tray_delegate());
   delegate->SetLoginStatus(LoginStatus::SUPERVISED);
 
   message_center::Notification* notification = GetPopup();
@@ -83,4 +83,4 @@ TEST_F(TraySupervisedUserInitialTest, SupervisedUserNoCrash) {
             notification->rich_notification_data().priority);
 }
 
-}  // namespace
+}  // namespace ash