Add DiscoveryNetworkMonitor implementation

chrome/browser/media/router/discovery/BUILD.gn

 # Copyright 2017 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.
 #
 
 static_library("discovery") {
   inputs = [
     "$root_gen_dir/chrome/grit/generated_resources.h",
   ]
   deps = [
@@ skipping 15 matching lines @@
     "dial/dial_media_sink_service.h",
     "dial/dial_registry.cc",
     "dial/dial_registry.h",
     "dial/dial_service.cc",
     "dial/dial_service.h",
     "dial/parsed_dial_device_description.cc",
     "dial/parsed_dial_device_description.h",
     "dial/safe_dial_device_description_parser.cc",
     "dial/safe_dial_device_description_parser.h",
   ]
+
+  if (!is_android) {
+    sources += [
+      "discovery_network_info.cc",
+      "discovery_network_info.h",
+      "discovery_network_list.h",
+      "discovery_network_list_posix.cc",
+      "discovery_network_list_wifi.h",
+      "discovery_network_list_wifi_linux.cc",
+      "discovery_network_list_win.cc",
+      "discovery_network_monitor.cc",
+      "discovery_network_monitor.h",
+    ]
+  }
 }