[cronet] Add a Builder class for UrlRequestContextConfig

components/cronet/url_request_context_config.cc

Index: components/cronet/url_request_context_config.cc
diff --git a/components/cronet/url_request_context_config.cc b/components/cronet/url_request_context_config.cc
index 78497f77d576d6776c4cbdebed70437c8fa14528..4878163e5ec3dfdb46602a9ae5df8a3a8cee26b4 100644
--- a/components/cronet/url_request_context_config.cc
+++ b/components/cronet/url_request_context_config.cc
@@ -392,4 +392,20 @@ void URLRequestContextConfig::ConfigureURLRequestContextBuilder(
   // 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