Add DiscoveryNetworkMonitor implementation

chrome/test/data/extensions/api_test/dial/experimental/network_id_changed.js

Index: chrome/test/data/extensions/api_test/dial/experimental/network_id_changed.js
diff --git a/chrome/test/data/extensions/api_test/dial/experimental/network_id_changed.js b/chrome/test/data/extensions/api_test/dial/experimental/network_id_changed.js
new file mode 100644
index 0000000000000000000000000000000000000000..559aced1cc3677a7a92d68180ab133fec941e2e4
--- /dev/null
+++ b/chrome/test/data/extensions/api_test/dial/experimental/network_id_changed.js
@@ -0,0 +1,19 @@
+// 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.
+
+let networkIds = [];
+
+chrome.dial.onNetworkIdChanged.addListener(networkId => {
+  chrome.test.assertFalse(networkId == "disconnected");
+  chrome.test.assertFalse(networkId == "unknown");
+  networkIds.push(networkId);
+  chrome.test.sendMessage("continue");
+
+  if (networkIds.length == 2) {
+    chrome.test.assertFalse(networkIds[0] == networkIds[1]);
+    chrome.test.succeed();
+  }
+});
+
+chrome.test.notifyPass();