Adding platform support check for NetworkObserver

net/base/network_change_notifier.cc

Index: net/base/network_change_notifier.cc
diff --git a/net/base/network_change_notifier.cc b/net/base/network_change_notifier.cc
index fb480e9705f2c418b32ca57a2e80888fd9c20aa0..cdf292fb560db58375116547678b4af1b4192bd9 100644
--- a/net/base/network_change_notifier.cc
+++ b/net/base/network_change_notifier.cc
@@ -634,7 +634,16 @@ double NetworkChangeNotifier::GetMaxBandwidthForConnectionSubtype(
 }
 
 // static
+bool NetworkChangeNotifier::AreNetworkHandlesSupported() {
+  if (g_network_change_notifier) {
+    return g_network_change_notifier->AreNetworkHandlesCurrentlySupported();
+  }
+  return false;
+}
+
+// static
 void NetworkChangeNotifier::GetConnectedNetworks(NetworkList* network_list) {
+  DCHECK(AreNetworkHandlesSupported());
   if (g_network_change_notifier) {
     g_network_change_notifier->GetCurrentConnectedNetworks(network_list);
   } else {
@@ -645,6 +654,7 @@ void NetworkChangeNotifier::GetConnectedNetworks(NetworkList* network_list) {
 // static
 NetworkChangeNotifier::ConnectionType
 NetworkChangeNotifier::GetNetworkConnectionType(NetworkHandle network) {
+  DCHECK(AreNetworkHandlesSupported());
   return g_network_change_notifier
              ? g_network_change_notifier->GetCurrentNetworkConnectionType(
                    network)
@@ -654,6 +664,7 @@ NetworkChangeNotifier::GetNetworkConnectionType(NetworkHandle network) {
 // static
 NetworkChangeNotifier::NetworkHandle
 NetworkChangeNotifier::GetDefaultNetwork() {
+  DCHECK(AreNetworkHandlesSupported());
   return g_network_change_notifier
              ? g_network_change_notifier->GetCurrentDefaultNetwork()
              : kInvalidNetworkHandle;
@@ -978,6 +989,10 @@ void NetworkChangeNotifier::GetCurrentMaxBandwidthAndConnectionType(
           : GetMaxBandwidthForConnectionSubtype(SUBTYPE_UNKNOWN);
 }
 
+bool NetworkChangeNotifier::AreNetworkHandlesCurrentlySupported() const {
+  return false;
+}
+
 void NetworkChangeNotifier::GetCurrentConnectedNetworks(
     NetworkList* network_list) const {
   network_list->clear();