Add support for custom entries in <cr_network_select/>.

ui/webui/resources/cr_elements/network/cr_network_list_types.js

Index: ui/webui/resources/cr_elements/network/cr_network_list_types.js
diff --git a/ui/webui/resources/cr_elements/network/cr_network_list_types.js b/ui/webui/resources/cr_elements/network/cr_network_list_types.js
new file mode 100644
index 0000000000000000000000000000000000000000..b0c21fba76da1838ae9ec540d155f62c99bf129d
--- /dev/null
+++ b/ui/webui/resources/cr_elements/network/cr_network_list_types.js
@@ -0,0 +1,22 @@
+// 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.
+
+/**
+ * @fileoverview
+ *
+ * This file contains typedefs <cr-network-list/> properties.
+ */
+
+var CrNetworkList = {};
+
+/**
+ * Generic managed property type. This should match any of the basic managed
+ * types in chrome.networkingPrivate, e.g. networkingPrivate.ManagedBoolean.
+ * @typedef {{
+ *   customItemName: (!String|undefined),
+ *   polymerIcon: (!String|undefined),
+ *   customData: (!Object|undefined),
+ * }}
+ */
+CrNetworkList.CustomItemState;