Break dependency of native_viewport_service on mojo::shell::Context

mojo/services/native_viewport/native_viewport_service.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_SERVICES_NATIVE_VIEWPORT_SERVICE_H_
 #define MOJO_SERVICES_NATIVE_VIEWPORT_SERVICE_H_
 
 #include "base/memory/scoped_vector.h"
 #include "mojo/public/cpp/application/application_impl.h"
 #include "mojo/services/native_viewport/native_viewport_export.h"
 #include "mojo/shell/context.h"
 
+namespace mojo {
+namespace services {
+
+class NativeViewportContext;
+
 MOJO_NATIVE_VIEWPORT_EXPORT mojo::ApplicationImpl*
     CreateNativeViewportService(
-        mojo::shell::Context* context,
-        mojo::ScopedMessagePipeHandle service_provider_handle);
+        NativeViewportContext* context,
+        ScopedMessagePipeHandle service_provider_handle);
+
+}  // namespace services
+}  // namespace mojo
 
 #endif  // MOJO_SERVICES_NATIVE_VIEWPORT_SERVICE_H_