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(DiscoveryNetworkList, GetDiscoveryNetworkIdList) {
+  auto network_ids = GetDiscoveryNetworkIdList();

[mark a. foltz, 2017/04/18 20:37:00]

It looks like you're not mocking anything out but assuming empty results are
returned.  Can you explain what you are testing?

[btolsch, 2017/04/20 04:03:50]

I am testing that the interface name and network ID are non-empty.  Since we
can't mock out the OS layer and therefore can't control what we get, this is all
we can really do.  I added comments explaining this and also changed the
expectations to hopefully be clearer.

+  for (const auto& network_id : network_ids) {
+    EXPECT_LT(0UL, network_id.interface_name.size());
+    EXPECT_LT(0UL, network_id.network_id.size());
+  }
+
+  auto interface_name_set = std::set<std::string>{};
+  std::transform(begin(network_ids), end(network_ids),
+                 std::insert_iterator<std::set<std::string>>{
+                     interface_name_set, end(interface_name_set)},
+                 [](const DiscoveryNetworkId& network_id) {
+                   return network_id.interface_name;
+                 });
+
+  EXPECT_EQ(interface_name_set.size(), network_ids.size());
+}