[net/dns] Isolate DnsConfigWatcher from DnsConfigService.

net/base/network_change_notifier_mac.h

Index: net/base/network_change_notifier_mac.h
diff --git a/net/base/network_change_notifier_mac.h b/net/base/network_change_notifier_mac.h
index ec2bb1fed50e97c42be5bf424f01e8e9117f9546..c95e952b873c2ef7a17cc24099e2168972784ac4 100644
--- a/net/base/network_change_notifier_mac.h
+++ b/net/base/network_change_notifier_mac.h
@@ -24,7 +24,7 @@ class NetworkChangeNotifierMac: public NetworkChangeNotifier {
   NetworkChangeNotifierMac();
   virtual ~NetworkChangeNotifierMac();
 
-  // NetworkChangeNotifier implementation:
+  // NetworkChangeNotifier:
   virtual bool IsCurrentlyOffline() const OVERRIDE;
 
  private:
@@ -34,6 +34,8 @@ class NetworkChangeNotifierMac: public NetworkChangeNotifier {
     ONLINE = 1
   };
 
+  class DnsWatcherThread;
+
   // Forwarder just exists to keep the NetworkConfigWatcherMac API out of
   // NetworkChangeNotifierMac's public API.
   class Forwarder : public NetworkConfigWatcherMac::Delegate {
@@ -83,6 +85,9 @@ class NetworkChangeNotifierMac: public NetworkChangeNotifier {
   Forwarder forwarder_;
   scoped_ptr<const NetworkConfigWatcherMac> config_watcher_;
 
+  // Thread on which we can run DnsConfigWatcher, which requires TYPE_IO.
+  scoped_ptr<DnsWatcherThread> dns_watcher_thread_;
+
   DISALLOW_COPY_AND_ASSIGN(NetworkChangeNotifierMac);
 };