Add DiscoveryNetworkMonitor implementation

chrome/browser/media/router/discovery/discovery_network_list_unittest.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.h"
+
+#include <algorithm>
+#include <iterator>
+#include <set>
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+TEST(DiscoveryNetworkListTest, GetDiscoveryNetworkInfoList) {
+  auto network_ids = GetDiscoveryNetworkInfoList();
+  for (const auto& network_id : network_ids) {
+    // We can't mock out the OS layer used by GetDiscoveryNetworkIdList, so
+    // instead just check that each returned interface name and ID is non-empty.
+    EXPECT_FALSE(network_id.name.empty());
+    EXPECT_FALSE(network_id.network_id.empty());
+  }
+
+  // Also check that at most one ID is returned per interface name.
+  auto interface_name_set = std::set<std::string>{};

[imcheng, 2017/05/26 23:49:01]

Can this just be std::set<std::string> interface_name_set; ?

[btolsch, 2017/05/30 09:54:30]

Done.

+  std::transform(begin(network_ids), end(network_ids),
+                 std::insert_iterator<std::set<std::string>>{
+                     interface_name_set, end(interface_name_set)},
+                 [](const DiscoveryNetworkInfo& network_info) {
+                   return network_info.name;
+                 });
+
+  EXPECT_EQ(interface_name_set.size(), network_ids.size());
+}