Promotes more accessors from WmShell to Shell

ash/common/system/user/tray_user.cc

Index: ash/common/system/user/tray_user.cc
diff --git a/ash/common/system/user/tray_user.cc b/ash/common/system/user/tray_user.cc
index c9035d3d84db5730af29909b682303fe25c0583a..b586fe914bd5d11579db7d9e24541ab4540e2acc 100644
--- a/ash/common/system/user/tray_user.cc
+++ b/ash/common/system/user/tray_user.cc
@@ -44,11 +44,11 @@ TrayUser::TrayUser(SystemTray* system_tray, UserIndex index)
       layout_view_(nullptr),
       avatar_(nullptr),
       label_(nullptr) {
-  WmShell::Get()->system_tray_notifier()->AddUserObserver(this);
+  Shell::Get()->system_tray_notifier()->AddUserObserver(this);
 }
 
 TrayUser::~TrayUser() {
-  WmShell::Get()->system_tray_notifier()->RemoveUserObserver(this);
+  Shell::Get()->system_tray_notifier()->RemoveUserObserver(this);
 }
 
 TrayUser::TestState TrayUser::GetStateForTest() const {