Fix potential crashes in NetworkHandler code

chromeos/network/network_state_handler_observer.cc

 // 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.
 
 #include "chromeos/network/network_state_handler_observer.h"
 
 namespace chromeos {
 
 NetworkStateHandlerObserver::NetworkStateHandlerObserver() {
 }
@@ skipping 19 matching lines @@
     const NetworkState* network) {
 }
 
 void NetworkStateHandlerObserver::DevicePropertiesUpdated(
     const chromeos::DeviceState* device) {
 }
 
 void NetworkStateHandlerObserver::ScanCompleted(const DeviceState* device) {
 }
 
-void NetworkStateHandlerObserver::IsShuttingDown() {
-}
+void NetworkStateHandlerObserver::OnShuttingDown() {}
 
 }  // namespace chromeos