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

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 45713b2966aade4acd0d1fb109bb89ca2af1250b..eec21d8644ec08b34399c4a58fe9e23c543d131f 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -419,6 +419,9 @@ const char kDownloadsNewUI[]                = "downloads-new-ui";
 // scripts.
 const char kDumpHistogramsOnExit[]          = "dump-histograms-on-exit";
 
+// Enables the experimental asynchronous DNS client.
+const char kEnableAsyncDns[]                = "enable-async-dns";
+
 // Enables AeroPeek for each tab. (This switch only works on Windows 7).
 const char kEnableAeroPeekTabs[]            = "enable-aero-peek-tabs";