[cronet] Add a Builder class for UrlRequestContextConfig

components/cronet/url_request_context_config.cc

 // 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.
 
 #include "components/cronet/url_request_context_config.h"
 
 #include <utility>
 
 #include "base/json/json_reader.h"
 #include "base/logging.h"
@@ skipping 374 matching lines @@
     cert_verifier = base::MakeUnique<net::CachingCertVerifier>(
         std::move(mock_cert_verifier));
   } else {
     // net::CertVerifier::CreateDefault() returns a CachingCertVerifier.
     cert_verifier = net::CertVerifier::CreateDefault();
   }
   context_builder->SetCertVerifier(std::move(cert_verifier));
   // TODO(mef): Use |config| to set cookies.
 }
 
+URLRequestContextConfigBuilder::URLRequestContextConfigBuilder() {}
+URLRequestContextConfigBuilder::~URLRequestContextConfigBuilder() {}
+
+std::unique_ptr<URLRequestContextConfig>
+URLRequestContextConfigBuilder::Build() {
+  std::unique_ptr<URLRequestContextConfig> config(new URLRequestContextConfig(

[mef, 2016/12/20 19:32:04]

nit: base::MakeUnique<T> is preferred:
https://cs.chromium.org/chromium/src/base/memory/ptr_util.h?rcl=1482236610&l=55

[lilyhoughton, 2016/12/20 21:31:40]

Done.

+      enable_quic, quic_user_agent_id, enable_spdy, enable_sdch, http_cache,
+      http_cache_max_size, load_disable_cache, storage_path, user_agent,
+      experimental_options, data_reduction_proxy_key,
+      data_reduction_primary_proxy, data_reduction_fallback_proxy,
+      data_reduction_secure_proxy_check_url, std::move(mock_cert_verifier),

[mef, 2016/12/20 19:32:04]

It seems that calling Build() more than once would produce valid equivalent
configs, except for |mock_cert_verifier| which is going to be moved into the
first one.

I think this is ok, but we should document it.

[lilyhoughton, 2016/12/20 21:31:40]

Done, documented in comment for |Build()| in .h

+      enable_network_quality_estimator,
+      bypass_public_key_pinning_for_local_trust_anchors, cert_verifier_data));
+  return config;
+}
+
 }  // namespace cronet