mash: remove more shell/shelf WmWindow usage.

ash/system/tray/system_tray_controller.cc

Index: ash/system/tray/system_tray_controller.cc
diff --git a/ash/system/tray/system_tray_controller.cc b/ash/system/tray/system_tray_controller.cc
index c2ba4b72bcaea78c05b316bedb3a6ddf5825420e..15db806d9023daad503aaf3ce1a0cbc8b03adef2 100644
--- a/ash/system/tray/system_tray_controller.cc
+++ b/ash/system/tray/system_tray_controller.cc
@@ -151,7 +151,7 @@ void SystemTrayController::SetClient(mojom::SystemTrayClientPtr client) {
 
 void SystemTrayController::SetPrimaryTrayEnabled(bool enabled) {
   ash::SystemTray* tray =
-      ShellPort::Get()->GetPrimaryRootWindowController()->GetSystemTray();
+      Shell::GetPrimaryRootWindowController()->GetSystemTray();
   if (!tray)
     return;
 
@@ -170,7 +170,7 @@ void SystemTrayController::SetPrimaryTrayEnabled(bool enabled) {
 
 void SystemTrayController::SetPrimaryTrayVisible(bool visible) {
   ash::SystemTray* tray =
-      ShellPort::Get()->GetPrimaryRootWindowController()->GetSystemTray();
+      Shell::GetPrimaryRootWindowController()->GetSystemTray();
   if (!tray)
     return;