Stop using shell::GetInstance()->system_tray() in system tray items

ash/system/chromeos/network/tray_vpn.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_CHROMEOS_NETWORK_TRAY_VPN_H
 #define ASH_SYSTEM_CHROMEOS_NETWORK_TRAY_VPN_H
 
 #include "ash/system/chromeos/network/network_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace ash {
 namespace internal {
 
 namespace tray {
 class NetworkDetailedView;
 class VpnDefaultView;
 class VpnDetailedView;
 }
 
 class TrayVPN : public SystemTrayItem,
                 public NetworkObserver {
  public:
-  TrayVPN();
+  explicit TrayVPN(SystemTray* system_tray);
   virtual ~TrayVPN();
 
   // Overridden from SystemTrayItem.
   virtual views::View* CreateTrayView(user::LoginStatus status) OVERRIDE;
   virtual views::View* CreateDefaultView(user::LoginStatus status) OVERRIDE;
   virtual views::View* CreateDetailedView(user::LoginStatus status) OVERRIDE;
   virtual views::View* CreateNotificationView(
       user::LoginStatus status) OVERRIDE;
   virtual void DestroyTrayView() OVERRIDE;
   virtual void DestroyDefaultView() OVERRIDE;
@@ skipping 17 matching lines @@
   tray::VpnDefaultView* default_;
   tray::NetworkDetailedView* detailed_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayVPN);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_NETWORK_TRAY_VPN_H