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

mojo/public/interfaces/application/service_provider.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.
 
 module mojo {
 
 // ServiceProvider is used to establish connections to services in a bi-
 // directional fashion between two applications.
 [Client=ServiceProvider]
 interface ServiceProvider {
   // Connect the given message pipe handle to the named service. If the named
   // service does not exist, then the handle will be closed.
-  ConnectToService(string interface_name, handle<message_pipe> pipe);
+  ConnectToService(string? interface_name, handle<message_pipe>? pipe);
 };
 
 }