Fix network portal detector crash on shutdown

chrome/browser/extensions/api/networking_private/networking_private_event_router_chromeos.cc

Index: chrome/browser/extensions/api/networking_private/networking_private_event_router_chromeos.cc
diff --git a/chrome/browser/extensions/api/networking_private/networking_private_event_router_chromeos.cc b/chrome/browser/extensions/api/networking_private/networking_private_event_router_chromeos.cc
index 5694c7e3ab8f2c8cd5efb45ff053c940ec619ece..b827f165883dd532e1fadd3ac8bce3db3534393a 100644
--- a/chrome/browser/extensions/api/networking_private/networking_private_event_router_chromeos.cc
+++ b/chrome/browser/extensions/api/networking_private/networking_private_event_router_chromeos.cc
@@ -132,11 +132,13 @@ void NetworkingPrivateEventRouterImpl::StartOrStopListeningForNetworkChanges() {
   if (should_listen && !listening_) {
     NetworkHandler::Get()->network_state_handler()->AddObserver(
         this, FROM_HERE);
-    NetworkPortalDetector::Get()->AddObserver(this);
+    if (chromeos::NetworkPortalDetector::IsInitialized())
+      NetworkPortalDetector::Get()->AddObserver(this);
   } else if (!should_listen && listening_) {
     NetworkHandler::Get()->network_state_handler()->RemoveObserver(
         this, FROM_HERE);
-    NetworkPortalDetector::Get()->RemoveObserver(this);
+    if (chromeos::NetworkPortalDetector::IsInitialized())
+      NetworkPortalDetector::Get()->RemoveObserver(this);
   }
   listening_ = should_listen;
 }