Add DiscoveryNetworkMonitor implementation

net/base/network_interfaces_linux.h

 // Copyright (c) 2014 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_INTERFACES_LINUX_H_
 #define NET_BASE_NETWORK_INTERFACES_LINUX_H_
 
 // This file is only used to expose some of the internals
 // of network_interfaces_linux.cc to address_tracker_linux and tests.
 
 #include <string>
 #include <unordered_set>
 
 #include "net/base/address_tracker_linux.h"
 #include "net/base/net_export.h"
 #include "net/base/network_interfaces.h"
 
 namespace net {
 namespace internal {
 
 typedef char* (*GetInterfaceNameFunction)(int interface_index, char* ifname);
 
 typedef std::string (*GetInterfaceSSIDFunction)(const std::string& ifname);
 
+NET_EXPORT std::string GetInterfaceSSID(const std::string& ifname);
+
 NET_EXPORT bool GetNetworkListImpl(
     NetworkInterfaceList* networks,
     int policy,
     const std::unordered_set<int>& online_links,
     const internal::AddressTrackerLinux::AddressMap& address_map,
     GetInterfaceNameFunction get_interface_name);
 
 // Gets the current Wi-Fi SSID based on |interfaces|. Returns
 // empty string if there are no interfaces or if two interfaces have different
 // connection types. Otherwise returns the SSID of all interfaces if they have
 // the same SSID. This is adapted from
 // NetworkChangeNotifier::ConnectionTypeFromInterfaceList.
 NET_EXPORT std::string GetWifiSSIDFromInterfaceListInternal(
     const NetworkInterfaceList& interfaces,
     internal::GetInterfaceSSIDFunction get_interface_ssid);
 
 }  // namespace internal
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_INTERFACES_LINUX_H_