[net/dns] Isolate DnsConfigWatcher from DnsConfigService.

net/dns/dns_config_watcher.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_WATCHER_H_
+#define NET_DNS_DNS_CONFIG_WATCHER_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace net {
+namespace internal {
+
+// Watches when the system DNS settings have changed. It is used by
+// NetworkChangeNotifier to provide signals to registered DNSObservers.
+// Depending on the platform, watches files, Windows registry, or libnotify key.
+// If some watches fail, we keep the working parts, but NetworkChangeNotifier
+// will mark notifications to DNSObserver with the CHANGE_DNS_WATCH_FAILED bit.
+class DnsConfigWatcher {
+ public:
+  DnsConfigWatcher();
+  ~DnsConfigWatcher();
+
+  // Starts watching system configuration for changes. The current thread must
+  // have a MessageLoopForIO. The signals will be delivered directly to
+  // the global NetworkChangeNotifier.
+  void Init();
+
+  // Must be called on the same thread as Init. Required if dtor will be called
+  // on a different thread.
+  void CleanUp();
+
+ private:
+  // Platform-specific implementation.
+  class Core;
+  scoped_ptr<Core> core_;
+
+  DISALLOW_COPY_AND_ASSIGN(DnsConfigWatcher);
+};
+
+}  // namespace internal
+}  // namespace net
+
+#endif  // NET_DNS_DNS_CONFIG_WATCHER_H_