Use URLRequestContextBuilderMojo to create the SystemURLRequestContext.

net/url_request/url_request_context_builder.h

 // 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.
 
 // This class is useful for building a simple URLRequestContext. Most creators
 // of new URLRequestContexts should use this helper class to construct it. Call
 // any configuration params, and when done, invoke Build() to construct the
 // URLRequestContext. This URLRequestContext will own all its own storage.
 //
 // URLRequestContextBuilder and its associated params classes are initially
@@ skipping 19 matching lines @@
 #include "net/base/net_export.h"
 #include "net/base/network_delegate.h"
 #include "net/base/proxy_delegate.h"
 #include "net/dns/host_resolver.h"
 #include "net/http/http_network_session.h"
 #include "net/net_features.h"
 #include "net/proxy/proxy_config_service.h"
 #include "net/proxy/proxy_service.h"
 #include "net/quic/core/quic_packets.h"
 #include "net/socket/next_proto.h"
+#include "net/ssl/ssl_config_service.h"
 #include "net/url_request/url_request_job_factory.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace net {
 
 class CertVerifier;
 class ChannelIDService;
@@ skipping 80 matching lines @@
   }
 
   // Sets the proxy service. If one is not provided, by default, uses system
   // libraries to evaluate PAC scripts, if available (And if not, skips PAC
   // resolution). Subclasses may override CreateProxyService for different
   // default behavior.
   void set_proxy_service(std::unique_ptr<ProxyService> proxy_service) {
     proxy_service_ = std::move(proxy_service);
   }
 
+  void set_ssl_config_service(
+      scoped_refptr<net::SSLConfigService> ssl_config_service) {
+    ssl_config_service_ = std::move(ssl_config_service);
+  }
+
   // Call these functions to specify hard-coded Accept-Language
   // or User-Agent header values for all requests that don't
   // have the headers already set.
   void set_accept_language(const std::string& accept_language) {
     accept_language_ = accept_language;
   }
   void set_user_agent(const std::string& user_agent) {
     user_agent_ = user_agent;
   }
 
@@ skipping 53 matching lines @@
   // custom factory will be unset and this must be called before the next Build
   // to set another custom one.
   void SetHttpAuthHandlerFactory(
       std::unique_ptr<HttpAuthHandlerFactory> factory);
 
   // By default HttpCache is enabled with a default constructed HttpCacheParams.
   void EnableHttpCache(const HttpCacheParams& params);
   void DisableHttpCache();
 
   // Override default HttpNetworkSession::Params settings.
   void set_http_network_session_params(

[Randy Smith (Not in Mondays), 2017/06/13 16:42:15]

Not for this CL, just commenting in case it's relevant at some future time: This
interface combined with all of the interfaces below that set member variables on
http_network_session_params_ strikes me a poorly designed--if the consumer
doesn't realize that calling this after any of the below interfaces will blow
away the effect of those interfaces, they could get a rude surprise that they
don't notice (depending on testing) for a while.

[mmenke, 2017/06/13 17:02:22]

I agree - it's on my imaginary TODO list to fix.

       const HttpNetworkSession::Params& http_network_session_params) {
     http_network_session_params_ = http_network_session_params;
   }
 
   void set_transport_security_persister_path(
       const base::FilePath& transport_security_persister_path) {
     transport_security_persister_path_ = transport_security_persister_path;
   }
 
   void SetSpdyAndQuicEnabled(bool spdy_enabled,
@@ skipping 129 matching lines @@
   HttpCacheParams http_cache_params_;
   HttpNetworkSession::Params http_network_session_params_;
   base::FilePath transport_security_persister_path_;
   NetLog* net_log_;
   std::unique_ptr<HostResolver> host_resolver_;
   std::unique_ptr<ChannelIDService> channel_id_service_;
   std::unique_ptr<ProxyConfigService> proxy_config_service_;
   bool pac_quick_check_enabled_;
   ProxyService::SanitizeUrlPolicy pac_sanitize_url_policy_;
   std::unique_ptr<ProxyService> proxy_service_;
+  scoped_refptr<net::SSLConfigService> ssl_config_service_;
   std::unique_ptr<NetworkDelegate> network_delegate_;
   std::unique_ptr<ProxyDelegate> proxy_delegate_;
   std::unique_ptr<CookieStore> cookie_store_;
   std::unique_ptr<HttpAuthHandlerFactory> http_auth_handler_factory_;
   std::unique_ptr<CertVerifier> cert_verifier_;
   std::unique_ptr<CTVerifier> ct_verifier_;
   std::vector<std::unique_ptr<URLRequestInterceptor>> url_request_interceptors_;
   std::unique_ptr<HttpServerProperties> http_server_properties_;
   std::map<std::string, std::unique_ptr<URLRequestJobFactory::ProtocolHandler>>
       protocol_handlers_;
 
   DISALLOW_COPY_AND_ASSIGN(URLRequestContextBuilder);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_CONTEXT_BUILDER_H_