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

mojo/services/native_viewport/native_viewport_mac.mm

 // 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.
 
 #include "mojo/services/native_viewport/native_viewport.h"
 
 #import <AppKit/NSApplication.h>
 #import <AppKit/NSView.h>
 #import <AppKit/NSWindow.h>
 
@@ skipping 61 matching lines @@
 
   NativeViewportDelegate* delegate_;
   NSWindow* window_;
   gfx::Rect rect_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeViewportMac);
 };
 
 // static
 scoped_ptr<NativeViewport> NativeViewport::Create(
-    shell::Context* context,
     NativeViewportDelegate* delegate) {
   return scoped_ptr<NativeViewport>(new NativeViewportMac(delegate)).Pass();
 }
 
 }  // namespace services
 }  // namespace mojo