Fix potential crashes in NetworkHandler code

chrome/browser/chromeos/proxy_config_service_impl.cc

Index: chrome/browser/chromeos/proxy_config_service_impl.cc
diff --git a/chrome/browser/chromeos/proxy_config_service_impl.cc b/chrome/browser/chromeos/proxy_config_service_impl.cc
index 4e63069a79562f6c5f95e8ff7b207f68ec309155..e5bd41ffbcbf064d4fc03dab78341488569baa0e 100644
--- a/chrome/browser/chromeos/proxy_config_service_impl.cc
+++ b/chrome/browser/chromeos/proxy_config_service_impl.cc
@@ -117,6 +117,13 @@ void ProxyConfigServiceImpl::DefaultNetworkChanged(
   DetermineEffectiveConfigFromDefaultNetwork();
 }
 
+void ProxyConfigServiceImpl::IsShuttingDown() {
+  // Ownership of this class is complicated. Stop observing NetworkStateHandler
+  // when the class shuts down.
+  NetworkHandler::Get()->network_state_handler()->RemoveObserver(this,
+                                                                 FROM_HERE);
+}
+
 // static
 bool ProxyConfigServiceImpl::IgnoreProxy(const PrefService* profile_prefs,
                                          const std::string network_profile_path,
@@ -167,6 +174,9 @@ bool ProxyConfigServiceImpl::IgnoreProxy(const PrefService* profile_prefs,
 }
 
 void ProxyConfigServiceImpl::DetermineEffectiveConfigFromDefaultNetwork() {
+  if (!NetworkHandler::IsInitialized())
+    return;
+
   NetworkStateHandler* handler = NetworkHandler::Get()->network_state_handler();
   const NetworkState* network = handler->DefaultNetwork();