[net] Adds AddressTrackerLinux which keeps track of interface addresses using rtnetlink.

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 9183532006d9dc658d939f8d7b0a7698773103e3..8c5f4461d96b66189d8de1c1a95fa7ac002830a6 100644
--- a/net/base/network_change_notifier.cc
+++ b/net/base/network_change_notifier.cc
@@ -84,6 +84,15 @@ NetworkChangeNotifier::GetConnectionType() {
       CONNECTION_UNKNOWN;
 }
 
+#if defined(OS_LINUX)
+// static
+const internal::AddressTrackerLinux*
+NetworkChangeNotifier::GetAddressTracker() {
+  return g_network_change_notifier ?
+        g_network_change_notifier->GetAddressTrackerInternal() : NULL;
+}
+#endif
+
 // static
 bool NetworkChangeNotifier::IsWatchingDNS() {
   if (!g_network_change_notifier)
@@ -155,6 +164,13 @@ NetworkChangeNotifier::NetworkChangeNotifier()
   g_network_change_notifier = this;
 }
 
+#if defined(OS_LINUX)
+const internal::AddressTrackerLinux*
+NetworkChangeNotifier::GetAddressTrackerInternal() const {
+  return NULL;
+}
+#endif
+
 // static
 void NetworkChangeNotifier::NotifyObserversOfIPAddressChange() {
   if (g_network_change_notifier) {