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

net/base/host_resolver.h

Index: net/base/host_resolver.h
diff --git a/net/base/host_resolver.h b/net/base/host_resolver.h
index 02b61af75d0f45a3afa4950474220bec3edd765a..e375961f47db81cf5382ca832e870bb4764a57b8 100644
--- a/net/base/host_resolver.h
+++ b/net/base/host_resolver.h
@@ -188,10 +188,12 @@ NET_EXPORT HostResolver* CreateNonCachingSystemHostResolver(
     size_t max_retry_attempts,
     NetLog* net_log);
 
-// Creates a HostResolver implementation that sends actual DNS queries to
-// the specified DNS server and parses response and returns results.
+// As above, but the HostResolver will use the asynchronous DNS client in
+// DnsTransaction, which will be configured using DnsConfigService to match
+// the system DNS settings. If the client fails, the resolver falls back to
+// the global HostResolverProc.
 NET_EXPORT HostResolver* CreateAsyncHostResolver(size_t max_concurrent_resolves,
-                                                 const IPAddressNumber& dns_ip,
+                                                 size_t max_retry_attempts,
                                                  NetLog* net_log);
 }  // namespace net