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

net/base/network_change_notifier_linux.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_BASE_NETWORK_CHANGE_NOTIFIER_LINUX_H_
 #define NET_BASE_NETWORK_CHANGE_NOTIFIER_LINUX_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "net/base/net_export.h"
 #include "net/base/network_change_notifier.h"
 
 namespace dbus {
 class Bus;
 }
 
 namespace net {
 
+namespace internal {
+class AddressTrackerLinux;
+}
+
 class NET_EXPORT_PRIVATE NetworkChangeNotifierLinux
     : public NetworkChangeNotifier {
  public:
   static NetworkChangeNotifierLinux* Create();
 
   // Unittests inject a mock bus.
   static NetworkChangeNotifierLinux* CreateForTest(dbus::Bus* bus);
 
  private:
+  friend class internal::AddressTrackerLinux;
   class Thread;
 
   explicit NetworkChangeNotifierLinux(dbus::Bus* bus);
   virtual ~NetworkChangeNotifierLinux();
 
   // NetworkChangeNotifier:
   virtual ConnectionType GetCurrentConnectionType() const OVERRIDE;
 
   // The thread used to listen for notifications.  This relays the notification
   // to the registered observers without posting back to the thread the object
   // was created on.
   // Also used for DnsConfigWatcher which requires TYPE_IO message loop.
   scoped_ptr<Thread> notifier_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkChangeNotifierLinux);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_CHANGE_NOTIFIER_LINUX_H_