Create native_viewport_service, don't build it into mojo_shell unless Android

mojo/shell/context.h

 // Copyright 2013 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.
 
 #ifndef MOJO_SHELL_CONTEXT_H_
 #define MOJO_SHELL_CONTEXT_H_
 
 #include <string>
 
 #include "mojo/application_manager/application_manager.h"
@@ skipping 25 matching lines @@
   ApplicationManager* application_manager() { return &application_manager_; }
   KeepAliveCounter* keep_alive_counter() { return &keep_alive_counter_; }
   MojoURLResolver* mojo_url_resolver() { return &mojo_url_resolver_; }
 
 #if defined(OS_ANDROID)
   base::MessageLoop* ui_loop() const { return ui_loop_; }
   void set_ui_loop(base::MessageLoop* ui_loop) { ui_loop_ = ui_loop; }
 #endif  // defined(OS_ANDROID)
 
  private:
-  class NativeViewportApplicationLoader;
-
   scoped_ptr<TaskRunners> task_runners_;
   ApplicationManager application_manager_;
   MojoURLResolver mojo_url_resolver_;
   scoped_ptr<Spy> spy_;
 #if defined(OS_ANDROID)
   base::MessageLoop* ui_loop_;
 #endif  // defined(OS_ANDROID)
 
   KeepAliveCounter keep_alive_counter_;
 
   DISALLOW_COPY_AND_ASSIGN(Context);
 };
 
 }  // namespace shell
 }  // namespace mojo
 
 #endif  // MOJO_SHELL_CONTEXT_H_