Move more from WmShell to Shell

ash/common/system/overview/overview_button_tray.cc

Index: ash/common/system/overview/overview_button_tray.cc
diff --git a/ash/common/system/overview/overview_button_tray.cc b/ash/common/system/overview/overview_button_tray.cc
index 2b7d243d2e182e975f610dda40cf126905129356..560769aff501230b16431908bdb5150d851cec1f 100644
--- a/ash/common/system/overview/overview_button_tray.cc
+++ b/ash/common/system/overview/overview_button_tray.cc
@@ -119,9 +119,9 @@ void OverviewButtonTray::UpdateIconVisibility() {
       !session_state_delegate->IsScreenLocked() &&
       session_state_delegate->GetSessionState() ==
           session_manager::SessionState::ACTIVE &&
-      shell->system_tray_delegate()->GetUserLoginStatus() !=
+      Shell::Get()->system_tray_delegate()->GetUserLoginStatus() !=
           LoginStatus::KIOSK_APP &&
-      shell->system_tray_delegate()->GetUserLoginStatus() !=
+      Shell::Get()->system_tray_delegate()->GetUserLoginStatus() !=
           LoginStatus::ARC_KIOSK_APP);
 }