Add a instance groups to Connect(), and introduce an Identity struct.

mojo/shell/tests/connect/connect_test.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 mojo.shell.test.mojom;
 
 interface ConnectTestService {
   GetTitle() => (string title);
 };
 
 // Interface implemented by a standalone (non-package) app.
 interface StandaloneApp {
   // Attempts to connect to an application whose name is explicitly allowed by
   // the standalone app's CapabilityFilter, but whose enclosing package is not.
   // The connection should be blocked and title should be "uninitialized".
   ConnectToAllowedAppInBlockedPackage() => (string title);
+
+  GetInstance() => (string instance);
 };
 
 struct ConnectionState {
   string connection_local_name;
   string connection_remote_name;
   string connection_remote_userid;
   uint32 connection_remote_id;
   string initialize_local_name;
   string initialize_userid;
   uint32 initialize_id;
 };
 
 interface ExposedInterface {
   ConnectionAccepted(ConnectionState state);
 };
 
 interface BlockedInterface {
   GetTitleBlocked() => (string blocked_title);
 };