[Cronet] Allow experimenting with Chrome's internal DNS resolver.

components/cronet/url_request_context_config_unittest.cc

 // 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.
 
 #include "components/cronet/url_request_context_config.h"
 
 #include "net/cert/cert_verifier.h"
 #include "net/http/http_network_session.h"
 #include "net/proxy/proxy_config.h"
 #include "net/proxy/proxy_config_service_fixed.h"
@@ skipping 20 matching lines @@
       false,
       // Storage path for http cache and cookie storage.
       "/data/data/org.chromium.net/app_cronet_test/test_storage",
       // User-Agent request header field.
       "fake agent",
       // JSON encoded experimental options.
       "{\"QUIC\":{\"store_server_configs_in_properties\":true,"
       "\"delay_tcp_race\":true,"
       "\"max_number_of_lossy_connections\":10,"
       "\"packet_loss_threshold\":0.5,"
-      "\"connection_options\":\"TIME,TBBR,REJ\"}}",
+      "\"connection_options\":\"TIME,TBBR,REJ\"},"
+      "\"AsyncDNS\":{\"enable\":true}}",
       // Data reduction proxy key.
       "",
       // Data reduction proxy.
       "",
       // Fallback data reduction proxy.
       "",
       // Data reduction proxy secure proxy check URL.
       "",
       // MockCertVerifier to use for testing purposes.
       scoped_ptr<net::CertVerifier>());
 
   net::URLRequestContextBuilder builder;
-  config.ConfigureURLRequestContextBuilder(&builder);
+  net::NetLog net_log;
+  config.ConfigureURLRequestContextBuilder(&builder, &net_log);
   // Set a ProxyConfigService to avoid DCHECK failure when building.
   builder.set_proxy_config_service(make_scoped_ptr(
       new net::ProxyConfigServiceFixed(net::ProxyConfig::CreateDirect())));
   scoped_ptr<net::URLRequestContext> context(builder.Build());
   const net::HttpNetworkSession::Params* params =
       context->GetNetworkSessionParams();
   // Check Quic Connection options.
   net::QuicTagVector quic_connection_options;
   quic_connection_options.push_back(net::kTIME);
   quic_connection_options.push_back(net::kTBBR);
   quic_connection_options.push_back(net::kREJ);
   EXPECT_EQ(quic_connection_options, params->quic_connection_options);
 
   // Check store_server_configs_in_properties.
   EXPECT_TRUE(params->quic_store_server_configs_in_properties);
 
   // Check delay_tcp_race.
   EXPECT_TRUE(params->quic_delay_tcp_race);
 
   // Check max_number_of_lossy_connections and packet_loss_threshold.
   EXPECT_EQ(10, params->quic_max_number_of_lossy_connections);
   EXPECT_FLOAT_EQ(0.5f, params->quic_packet_loss_threshold);
+
+  // Check AsyncDNS resolver is enabled.
+  EXPECT_NE(nullptr, context->host_resolver()->GetDnsConfigAsValue());
 }
 
 }  // namespace cronet