[net] HostResolverImpl + DnsTransaction + DnsConfigService = Asynchronous DNS ready for experiments.

chrome/browser/io_thread.cc

Index: chrome/browser/io_thread.cc
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index 6ad01f64ac68477963aef845ca567c9f7517cc48..4575188b464e29afbb08cea1ed3f6b2d8ac58516 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -141,14 +141,19 @@ net::HostResolver* CreateGlobalHostResolver(net::NetLog* net_log) {
       command_line.GetSwitchValueASCII(switches::kDnsServer);
     net::IPAddressNumber dns_ip_number;
     if (net::ParseIPLiteralToNumber(dns_ip_string, &dns_ip_number)) {
-      global_host_resolver =
-        net::CreateAsyncHostResolver(parallelism, dns_ip_number, net_log);
+      // TODO(szym): Somehow pass |dns_ip_number| to the DnsConfigService.
+      LOG(WARNING) << "Configuration currently ignored --dns-server";
     } else {
       LOG(ERROR) << "Invalid IP address specified for --dns-server: "
                  << dns_ip_string;
     }
   }
 
+  if (command_line.HasSwitch(switches::kEnableAsyncDns)) {
+    global_host_resolver =
+        net::CreateAsyncHostResolver(parallelism, retry_attempts, net_log);
+  }
+
   if (!global_host_resolver) {
     global_host_resolver =
       net::CreateSystemHostResolver(parallelism, retry_attempts, net_log);