Add DiscoveryNetworkMonitor implementation

chrome/browser/media/router/discovery/discovery_network_list_wifi_linux.cc

+// Copyright (c) 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.
+
+#include "chrome/browser/media/router/discovery/discovery_network_list_wifi.h"
+
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <linux/wireless.h>
+
+#include "base/logging.h"
+#include "net/base/network_interfaces_linux.h"
+
+bool MaybeGetWifiSSID(const char* if_name, std::string* ssid) {
+  DCHECK(if_name);
+
+  auto maybe_ssid = net::internal::GetInterfaceSSID(if_name);
+  if (maybe_ssid.size() > 0) {
+    *ssid = std::move(maybe_ssid);
+    return true;
+  }
+  return false;
+}