Reland: chromeos: Convert ash VPNDelegate interface to mojo

ash/public/interfaces/vpn_list.mojom

+// 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.
+
+module ash.mojom;
+
+// Describes a third-party VPN provided by an extension (e.g. Cisco AnyConnect).
+struct ThirdPartyVpnProvider {
+  string name;
+  string extension_id;
+};
+
+// Manages the VPN provider list in ash. Allows extension-backed VPN providers
+// to be added. Ash handles the built-in OpenVPN / L2TP provider internally.
+interface VpnList {
+  // Sets the list of third-party VPN providers. The |providers| array may be
+  // empty to clear the list (e.g. after the last third-party VPN extension is
+  // uninstalled).
+  SetThirdPartyVpnProviders(array<ThirdPartyVpnProvider> providers);
+};