Use URLRequestContextBuilderMojo to create the SystemURLRequestContext.

net/url_request/url_request_context_builder.cc

 // Copyright (c) 2012 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 "net/url_request/url_request_context_builder.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 318 matching lines @@
     context->set_net_log(net_log_);
   } else {
     storage->set_net_log(base::WrapUnique(new NetLog));
   }
 
   if (!host_resolver_) {
     host_resolver_ = HostResolver::CreateDefaultResolver(context->net_log());
   }
   storage->set_host_resolver(std::move(host_resolver_));
 
-  storage->set_ssl_config_service(new SSLConfigServiceDefaults);
+  if (ssl_config_service_) {
+    // This takes a raw pointer, but |storage| will hold onto a reference to the
+    // service.
+    storage->set_ssl_config_service(ssl_config_service_.get());
+  } else {
+    storage->set_ssl_config_service(new SSLConfigServiceDefaults);
+  }
 
   if (!http_auth_handler_factory_) {
     http_auth_handler_factory_ =
         HttpAuthHandlerRegistryFactory::CreateDefault(context->host_resolver());
   }
 
   storage->set_http_auth_handler_factory(std::move(http_auth_handler_factory_));
 
   if (cookie_store_set_by_client_) {
     storage->set_cookie_store(std::move(cookie_store_));
@@ skipping 155 matching lines @@
     std::unique_ptr<ProxyConfigService> proxy_config_service,
     URLRequestContext* url_request_context,
     HostResolver* host_resolver,
     NetworkDelegate* network_delegate,
     NetLog* net_log) {
   return ProxyService::CreateUsingSystemProxyResolver(
       std::move(proxy_config_service), net_log);
 }
 
 }  // namespace net