Convert //ash from scoped_ptr to std::unique_ptr

ash/system/chromeos/network/tray_vpn.h

Index: ash/system/chromeos/network/tray_vpn.h
diff --git a/ash/system/chromeos/network/tray_vpn.h b/ash/system/chromeos/network/tray_vpn.h
index 4b22966d4d5d998f08d107dbe442490af95ec20a..cf11b35e8eebeba5a8988e053c4865c381b2a22b 100644
--- a/ash/system/chromeos/network/tray_vpn.h
+++ b/ash/system/chromeos/network/tray_vpn.h
@@ -5,10 +5,11 @@
 #ifndef ASH_SYSTEM_CHROMEOS_NETWORK_TRAY_VPN_H
 #define ASH_SYSTEM_CHROMEOS_NETWORK_TRAY_VPN_H
 
+#include <memory>
+
 #include "ash/system/chromeos/network/tray_network_state_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
 
 namespace ash {
 class TrayNetworkStateObserver;
@@ -41,7 +42,7 @@ class TrayVPN : public SystemTrayItem,
  private:
   tray::VpnDefaultView* default_;
   tray::NetworkDetailedView* detailed_;
-  scoped_ptr<TrayNetworkStateObserver> network_state_observer_;
+  std::unique_ptr<TrayNetworkStateObserver> network_state_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayVPN);
 };