Detect domain-specific resolvers on OS X and disable DnsClient in such cases.

chrome/browser/net/dns_probe_service.cc

 // Copyright (c) 2012 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 "chrome/browser/net/dns_probe_service.h"
 
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
 #include "net/base/ip_endpoint.h"
@@ skipping 116 matching lines @@
 void DnsProbeService::ClearCachedResultForTesting() {
   ClearCachedResult();
 }
 
 void DnsProbeService::SetSystemClientToCurrentConfig() {
   DnsConfig system_config;
   NetworkChangeNotifier::GetDnsConfig(&system_config);
   system_config.search.clear();
   system_config.attempts = 1;
   system_config.randomize_ports = false;
+  system_config.unhandled_options = false;

[mmenke, 2013/08/19 14:12:04]

Wonder if we should just skip the probe in this case...  Not a concern for this
CL.

[szym, 2013/08/19 14:26:16]

What does the prober do if there's no system config? If it fails gracefully,
I'll remove this line.

[mmenke, 2013/08/19 14:54:03]

DnsProbeRunner::RunProbe checks if the transaction factory is NULL, and if so,
passes along an "unknown" result.

[szym, 2013/08/20 18:55:34]

Removed.

 
   scoped_ptr<DnsClient> system_client(DnsClient::CreateClient(NULL));
   system_client->SetConfig(system_config);
 
   system_runner_.SetClient(system_client.Pass());
 }
 
 void DnsProbeService::SetPublicClientToGooglePublicDns() {
   DnsConfig public_config;
   public_config.nameservers.push_back(MakeDnsEndPoint(kGooglePublicDns1));
@@ skipping 63 matching lines @@
 bool DnsProbeService::CachedResultIsExpired() const {
   if (state_ != STATE_RESULT_CACHED)
     return false;
 
   const base::TimeDelta kMaxResultAge =
       base::TimeDelta::FromMilliseconds(kMaxResultAgeMs);
   return base::Time::Now() - probe_start_time_ > kMaxResultAge;
 }
 
 }  // namespace chrome_browser_net