Remove Client relationship between mojo.Shell/mojo.Application

shell/app_child_process.mojom

 // Copyright 2014 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;
 
+import "mojo/public/interfaces/application/application.mojom";
+
 [Client=AppChildControllerClient]
 interface AppChildController {
-  // TODO(vtl): |service| should be of a more specific type.
-  StartApp(string app_path, handle<message_pipe> service);
+  StartApp(string app_path, mojo.Application& application_request);
 };
 
 interface AppChildControllerClient {
   AppCompleted(int32 result);
 };