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

net/base/network_change_notifier.h

Index: net/base/network_change_notifier.h
diff --git a/net/base/network_change_notifier.h b/net/base/network_change_notifier.h
index 8420a8f5477c7d03e4cccb6e1c555b179630fb67..192aa9a47583b968cdb8d75482034eb597ef4357 100644
--- a/net/base/network_change_notifier.h
+++ b/net/base/network_change_notifier.h
@@ -16,6 +16,10 @@ class NetworkChangeNotifierFactory;
 
 namespace internal {
 class DnsConfigWatcher;
+
+#if defined(OS_LINUX)
+class AddressTrackerLinux;
+#endif
 }
 
 // NetworkChangeNotifier monitors the system for network changes, and notifies
@@ -124,6 +128,11 @@ class NET_EXPORT NetworkChangeNotifier {
   // attempt to a particular remote site will be successful.
   static ConnectionType GetConnectionType();
 
+#if defined(OS_LINUX)
+  // Returns the AddressTrackerLinux if present.
+  static const internal::AddressTrackerLinux* GetAddressTracker();
+#endif
+
   // Convenience method to determine if the user is offline.
   // Returns true if there is currently no internet connection.
   //