Mojom: Blanket change to mark all pointer/handle fields as nullable.

mojo/services/public/interfaces/network/network_service.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/services/public/interfaces/network/cookie_store.mojom"
 import "mojo/services/public/interfaces/network/url_loader.mojom"
 
 module mojo {
 
 interface NetworkService {
-  CreateURLLoader(URLLoader& loader);
+  CreateURLLoader(URLLoader&? loader);
 
-  GetCookieStore(CookieStore& cookie_store);
+  GetCookieStore(CookieStore&? cookie_store);
 
   // TODO(darin): Add other methods here.
 };
 
 }