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

net/dns/dns_config_service.h

 // 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.
 
 #ifndef NET_DNS_DNS_CONFIG_SERVICE_H_
 #define NET_DNS_DNS_CONFIG_SERVICE_H_
 #pragma once
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/file_path.h"
 #include "base/gtest_prod_util.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/time.h"
 #include "net/base/ip_endpoint.h"  // win requires size of IPEndPoint
 #include "net/base/net_export.h"
 #include "net/dns/dns_hosts.h"
 #include "net/dns/serial_worker.h"
 
 namespace net {
 
@@ skipping 32 matching lines @@
   int attempts;
   // Round robin entries in |nameservers| for subsequent requests.
   bool rotate;
   // Enable EDNS0 extensions.
   bool edns0;
 };
 
 
 // Service for watching when the system DNS settings have changed.
 // Depending on the platform, watches files in /etc/ or win registry.
+// This class also serves as the do-nothing mock implementation.
 class NET_EXPORT_PRIVATE DnsConfigService
   : NON_EXPORTED_BASE(public base::NonThreadSafe) {
  public:
   // Callback interface for the client. The observer is called on the same
   // thread as Watch(). Observer must outlive the service.
   class Observer {
    public:
     virtual ~Observer() {}
 
     // Called only when |dns_config| is different from the last call.
     virtual void OnConfigChanged(const DnsConfig& dns_config) = 0;
   };
 
   // Creates the platform-specific DnsConfigService.
-  static DnsConfigService* CreateSystemService();
+  static scoped_ptr<DnsConfigService> CreateSystemService();
 
   DnsConfigService();
   virtual ~DnsConfigService();
 
   // Immediately starts watching system configuration for changes and attempts
   // to read the configuration. For some platform implementations, the current
   // thread must have an IO loop (for base::files::FilePathWatcher).
   virtual void Watch() {}
 
   // If a config is available, |observer| will immediately be called with
@@ skipping 38 matching lines @@
   // Written in DoRead, read in OnReadFinished, no locking necessary.
   DnsHosts dns_hosts_;
   bool success_;
 
   DISALLOW_COPY_AND_ASSIGN(DnsHostsReader);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_CONFIG_SERVICE_H_