mozart: Introduce new view manager interfaces.

mojo/services/ui/views/interfaces/view_provider.mojom

+// Copyright 2015 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.
+
+[DartPackage="mojo_services"]
+module mojo.ui;
+
+import "mojo/public/interfaces/application/service_provider.mojom";
+import "mojo/services/ui/views/interfaces/views.mojom";
+
+// Provides a View upon request.
+//
+// Applications should implement and expose this service so that they can
+// expose views to be embedded into other applications.
+interface ViewProvider {
+  // Creates and registers a view with the view manager and returns its
+  // view token (as provided by |ViewManager.RegisterView()|).
+  //
+  // Having received the view token, the caller should attach the view to
+  // a view tree and lay it out.
+  //
+  // The caller may provide services to the view via the |services|
+  // service provider.
+  //
+  // The caller may receive services from the view via the |exposed_services|
+  // service provider.
+  CreateView(mojo.ServiceProvider&? services,
+             mojo.ServiceProvider? exposed_services) =>
+                 (ViewToken view_token);
+};