Add DiscoveryNetworkMonitor implementation

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

Index: chrome/browser/media/router/discovery/BUILD.gn
diff --git a/chrome/browser/media/router/discovery/BUILD.gn b/chrome/browser/media/router/discovery/BUILD.gn
index 21199e1256b57de557877a972fafae8d49e09d87..6a16b26cfebf6722bf7abb8b02cabcfce1fa42a4 100644
--- a/chrome/browser/media/router/discovery/BUILD.gn
+++ b/chrome/browser/media/router/discovery/BUILD.gn
@@ -33,4 +33,17 @@ static_library("discovery") {
     "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_monitor.cc",
+      "discovery_network_monitor.h",
+    ]
+  }
 }