Revert 40099 - Revert 39998 Revert 39996 Refine IPv6 probe to require that ...

chrome/browser/io_thread.cc

 // Copyright (c) 2010 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/io_thread.h"
 #include "base/command_line.h"
 #include "base/leak_tracker.h"
 #include "base/logging.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_thread.h"
 #include "chrome/browser/net/dns_global.h"
 #include "chrome/browser/net/url_fetcher.h"
 #include "chrome/common/chrome_switches.h"
 #include "net/base/mapped_host_resolver.h"
 #include "net/base/host_cache.h"
 #include "net/base/host_resolver.h"
 #include "net/base/host_resolver_impl.h"
 #include "net/base/net_util.h"
 #include "net/base/network_change_notifier.h"
 #include "net/http/http_auth_handler_factory.h"
 #include "net/url_request/url_request.h"
 
 namespace {
 
 net::HostResolver* CreateGlobalHostResolver(
     net::NetworkChangeNotifier* network_change_notifier) {
+  net::HostResolver* global_host_resolver = NULL;
+
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
-  net::HostResolver* global_host_resolver =
+
+  global_host_resolver =
       net::CreateSystemHostResolver(network_change_notifier);
 
-  // Determine if we should disable IPv6 support.
   if (!command_line.HasSwitch(switches::kEnableIPv6)) {
-    if (command_line.HasSwitch(switches::kDisableIPv6)) {
+    // Measure impact of allowing IPv6 support without probing.
+    const FieldTrial::Probability kDivisor = 100;
+    const FieldTrial::Probability kProbability = 50;  // 50% probability.
+    FieldTrial* trial = new FieldTrial("IPv6_Probe", kDivisor);
+    int skip_group = trial->AppendGroup("_IPv6_probe_skipped", kProbability);
+    trial->AppendGroup("_IPv6_probe_done",
+                       FieldTrial::kAllRemainingProbability);
+    bool use_ipv6_probe = (trial->group() != skip_group);
+
+    // Perform probe, and then optionally use result to disable IPv6.
+    // Some users report confused OS handling of IPv6, leading to large
+    // latency.  If we can show that IPv6 is not supported, then disabliing it
+    // will work around such problems.
+    if ((!net::IPv6Supported() && use_ipv6_probe) ||
+        command_line.HasSwitch(switches::kDisableIPv6))
       global_host_resolver->SetDefaultAddressFamily(net::ADDRESS_FAMILY_IPV4);
-    } else {
-      net::HostResolverImpl* host_resolver_impl =
-          global_host_resolver->GetAsHostResolverImpl();
-      if (host_resolver_impl != NULL) {
-        // (optionally) Use probe to decide if support is warranted.
-
-        // Measure impact of probing to allow IPv6.
-        // Some users report confused OS handling of IPv6, leading to large
-        // latency.  If we can show that IPv6 is not supported, then disabliing
-        // it will work around such problems.
-        const FieldTrial::Probability kDivisor = 100;
-        const FieldTrial::Probability kProbability = 50;  // 50% probability.
-        FieldTrial* trial = new FieldTrial("IPv6_Probe", kDivisor);
-        int skip_group = trial->AppendGroup("_IPv6_probe_skipped",
-                                            kProbability);
-        trial->AppendGroup("_IPv6_probe_done",
-                           FieldTrial::kAllRemainingProbability);
-        bool use_ipv6_probe = (trial->group() != skip_group);
-        if (use_ipv6_probe)
-          host_resolver_impl->ProbeIPv6Support();
-      }
-    }
   }
 
   // If hostname remappings were specified on the command-line, layer these
   // rules on top of the real host resolver. This allows forwarding all requests
   // through a designated test server.
-  if (!command_line.HasSwitch(switches::kHostResolverRules))
-    return global_host_resolver;
+  if (command_line.HasSwitch(switches::kHostResolverRules)) {
+    net::MappedHostResolver* remapped_resolver =
+        new net::MappedHostResolver(global_host_resolver);
+    global_host_resolver = remapped_resolver;
+    remapped_resolver->SetRulesFromString(
+        command_line.GetSwitchValueASCII(switches::kHostResolverRules));
+  }
 
-  net::MappedHostResolver* remapped_resolver =
-      new net::MappedHostResolver(global_host_resolver);
-  remapped_resolver->SetRulesFromString(
-      command_line.GetSwitchValueASCII(switches::kHostResolverRules));
-  return remapped_resolver;
+  return global_host_resolver;
 }
 
 }  // namespace
 
 // The IOThread object must outlive any tasks posted to the IO thread before the
 // Quit task.
 template <>
 struct RunnableMethodTraits<IOThread> {
   void RetainCallee(IOThread* /* io_thread */) {}
   void ReleaseCallee(IOThread* /* io_thread */) {}
@@ skipping 134 matching lines @@
 
   // Clear the host cache to avoid showing entries from the OTR session
   // in about:net-internals.
   if (globals_->host_resolver->GetAsHostResolverImpl()) {
     net::HostCache* host_cache =
         globals_->host_resolver.get()->GetAsHostResolverImpl()->cache();
     if (host_cache)
       host_cache->clear();
   }
 }