chromeos: Refactor ash SystemTrayDelegate enterprise methods to mojo

ash/system/enterprise/tray_enterprise.h

Index: ash/system/enterprise/tray_enterprise.h
diff --git a/ash/system/enterprise/tray_enterprise.h b/ash/system/enterprise/tray_enterprise.h
index 72f044039f2a1010dddfe406b6fcef4fabfa50ef..b00ef685c2f42c893b79be1aa7f894d1ea4e5b95 100644
--- a/ash/system/enterprise/tray_enterprise.h
+++ b/ash/system/enterprise/tray_enterprise.h
@@ -14,6 +14,8 @@ 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 {
@@ -35,6 +37,8 @@ class TrayEnterprise : public SystemTrayItem,
   // Overridden from ViewClickListener.
   void OnViewClicked(views::View* sender) override;
 
+  LabelTrayView* tray_view() { return tray_view_; }
+
  private:
   LabelTrayView* tray_view_;