Add test for system tray network menu icon for extension-controlled networks

chrome/test/data/extensions/networking_config_delegate/background.js

+// Copyright 2016 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.
+
+// Register this extension as the network handler for wifi1.
+chrome.networking.config.setNetworkFilter([{Type: 'WiFi', SSID: 'wifi1'}],
+                                          function() {
+                                            chrome.test.sendMessage('done');
+                                          });