chromeos: Remove some WmWindow usage from ash/system

ash/system/tray/system_tray_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/system/tray/system_tray_controller.h"
 
 #include "ash/root_window_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_port.h"
 #include "ash/system/tray/system_tray.h"
@@ skipping 182 matching lines @@
     bool active_directory_managed) {
   enterprise_domain_ = enterprise_domain;
   active_directory_managed_ = active_directory_managed;
   Shell::Get()->system_tray_notifier()->NotifyEnterpriseDomainChanged();
 }
 
 void SystemTrayController::ShowUpdateIcon(mojom::UpdateSeverity severity,
                                           bool factory_reset_required,
                                           mojom::UpdateType update_type) {
   // Show the icon on all displays.
-  for (WmWindow* root : ShellPort::Get()->GetAllRootWindows()) {
-    ash::SystemTray* tray = root->GetRootWindowController()->GetSystemTray();
+  for (RootWindowController* root : Shell::GetAllRootWindowControllers()) {
+    ash::SystemTray* tray = root->GetSystemTray();
     // External monitors might not have a tray yet.
     if (!tray)
       continue;
     tray->tray_update()->ShowUpdateIcon(severity, factory_reset_required,
                                         update_type);
   }
 }
 
 }  // namespace ash