Replace //net TypeConverters with StructTraits.

net/interfaces/host_resolver_service.mojom

 // Copyright 2015 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.
 
 // WARNING! Do NOT use this mojom. It is intended as a temporary interface to
 // implement out-of-process proxy resolution. If you wish to use a Mojo DNS
 // service, contact amistry@/sammc@ and net-dev to discuss a permanent Mojo DNS
 // interface.
 
 // Put Mojo definitions into their own namespace to avoid collisions with C++
@@ skipping 24 matching lines @@
   uint16 port;
 };
 
 // Mirror of net::AddressList.
 struct AddressList {
   array<IPEndPoint> addresses;
 };
 
 interface HostResolverRequestClient {
   // |error| is a value in net::Error.
-  ReportResult(int32 error, AddressList? result);
+  ReportResult(int32 error, AddressList result);
 };