Fix potential crashes in NetworkHandler code

chrome/browser/chromeos/login/screens/network_screen.cc

Index: chrome/browser/chromeos/login/screens/network_screen.cc
diff --git a/chrome/browser/chromeos/login/screens/network_screen.cc b/chrome/browser/chromeos/login/screens/network_screen.cc
index 4f8c8089c922a7c5e703a307a24f312f7ab0f782..b10458f7e48a088735d4caf0bb16da74ecbbe4c0 100644
--- a/chrome/browser/chromeos/login/screens/network_screen.cc
+++ b/chrome/browser/chromeos/login/screens/network_screen.cc
@@ -118,6 +118,9 @@ void NetworkScreen::OnViewDestroyed(NetworkView* view) {
   if (view_ == view) {
     view_ = nullptr;
     timezone_subscription_.reset();
+    // Ownership of NetworkScreen is complicated; ensure that we remove
+    // this as a NetworkStateHandler observer when the view is destroyed.
+    UnsubscribeNetworkNotification();
   }
 }