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/files/scoped_file.h"
+#include "base/logging.h"
+#include "net/base/network_interfaces_linux.h"
+
+bool MaybeGetWifiSSID(const std::string& if_name, std::string* ssid_out) {
+  DCHECK(ssid_out);
+
+  base::ScopedFD ioctl_socket(socket(AF_INET, SOCK_DGRAM, 0));
+  if (!ioctl_socket.is_valid())
+    return false;
+  struct iwreq wreq = {};
+  strncpy(wreq.ifr_name, if_name.data(), IFNAMSIZ - 1);
+
+  char ssid[IW_ESSID_MAX_SIZE + 1] = {0};
+  wreq.u.essid.pointer = ssid;
+  wreq.u.essid.length = IW_ESSID_MAX_SIZE;
+  if (ioctl(ioctl_socket.get(), SIOCGIWESSID, &wreq) == -1) {
+    return false;
+  }
+  if (ssid[0] != 0) {
+    ssid_out->assign(ssid);
+    return true;
+  }
+  return false;
+}