Replace more ObserverList with base::ObserverList.

ash/system/chromeos/network/vpn_delegate.h

 // Copyright 2015 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_VPN_DELEGATE_H
 #define ASH_SYSTEM_CHROMEOS_NETWORK_VPN_DELEGATE_H
 
 #include <string>
 #include <vector>
 
@@ skipping 73 matching lines @@
 
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);
 
  protected:
   // Notify observers that the list of VPN providers enabled in the primary
   // user's profile has changed.
   void NotifyObservers();
 
  private:
-  ObserverList<Observer, true> observer_list_;
+  base::ObserverList<Observer, true> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(VPNDelegate);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_NETWORK_VPN_DELEGATE_H