Turn 'browser' app into a 'launcher_ui' app that window_manager embeds.

mojo/services/navigation/navigation.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.
 
 import "../public/interfaces/network/url_loader.mojom"
 
 module mojo.navigation {
 
 struct NavigationDetails {
   string url;
   mojo.URLResponse response;
   handle<data_pipe_consumer> response_body_stream;
 
   // TODO(aa): method, data, etc.
 };
 
+// Embedders that support navigation of implement this interface.
+interface NavigatorHost {
+  RequestNavigate(uint32 source_node_id, NavigationDetails details);
+};
+
 // Applications implement this interface to support navigation of their views
 // by embedders.
 interface Navigator {
   Navigate(uint32 node_id, NavigationDetails details);
 };
 
 }