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 client interface (usually provided by chrome browser).
+  SetClient(VpnListClient client);

[stevenjb, 2016/11/19 00:04:58]

This just seems confusing to me. It seems like the Show methods should just be
part of whatever client handles "show UI" calls (e.g. "show settings"). There's
no real need to associate that with the model.

+
+  // 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);
+};
+
+// Allows ash to make requests of chrome browser, e.g. to show webui settings.
+interface VpnListClient {
+  // Shows the configuration page for the built-in OpenVPN / L2TP provider.
+  ShowBuiltInAddNetworkPage();
+
+  // Shows the configuration page for a third-party VPN. |extension_id| must be
+  // a valid, non-empty extension ID.
+  ShowThirdPartyAddNetworkPage(string extension_id);

[stevenjb, 2016/11/19 00:04:58]

In theory we could make this a single method, with an empty extension_id
indicating "built in"...

+};