chromeos: Refactor ash SystemTrayDelegate enterprise methods to mojo

ash/system/enterprise/tray_enterprise.h

 // Copyright (c) 2012 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.
 
 #ifndef ASH_SYSTEM_ENTERPRISE_TRAY_ENTERPRISE_H_
 #define ASH_SYSTEM_ENTERPRISE_TRAY_ENTERPRISE_H_
 
 #include "ash/system/enterprise/enterprise_domain_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "ash/system/tray/view_click_listener.h"
 #include "base/macros.h"
 
 namespace ash {
 class LabelTrayView;
 class SystemTray;
 
+// System tray item that shows a message ("This device managed by example.com")
+// in the tray menu for enterprise enrolled devices.
 class TrayEnterprise : public SystemTrayItem,
                        public ViewClickListener,
                        public EnterpriseDomainObserver {
  public:
   explicit TrayEnterprise(SystemTray* system_tray);
   ~TrayEnterprise() override;
 
   // If message is not empty updates content of default view, otherwise hides
   // tray items.
   void UpdateEnterpriseMessage();
 
   // Overridden from SystemTrayItem.
   views::View* CreateDefaultView(LoginStatus status) override;
   void DestroyDefaultView() override;
 
   // Overridden from EnterpriseDomainObserver.
   void OnEnterpriseDomainChanged() override;
 
   // Overridden from ViewClickListener.
   void OnViewClicked(views::View* sender) override;
 
+  LabelTrayView* tray_view() { return tray_view_; }
+
  private:
   LabelTrayView* tray_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayEnterprise);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_ENTERPRISE_TRAY_ENTERPRISE_H_