Make the ServiceProvider& arg to GetServiceProviderForFrame non-nullable.

content/common/render_frame_setup.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 "../../mojo/public/interfaces/application/service_provider.mojom"
 
 module content {
 
 interface RenderFrameSetup {
   GetServiceProviderForFrame(int32 frame_routing_id,
-                             mojo.ServiceProvider&? service_provider);
+                             mojo.ServiceProvider& service_provider);
 };
 
 }