Revert 99666 (sync tests started failing on mac10.6:

net/base/network_change_notifier.h

Index: net/base/network_change_notifier.h
===================================================================
--- net/base/network_change_notifier.h	(revision 99676)
+++ net/base/network_change_notifier.h	(working copy)
@@ -50,22 +50,6 @@
     DISALLOW_COPY_AND_ASSIGN(OnlineStateObserver);
   };
 
-  class NET_EXPORT DNSObserver {
-   public:
-    virtual ~DNSObserver() {}
-
-    // Will be called when the DNS resolver of the system may have changed.
-    // This is only used on Linux currently and watches /etc/resolv.conf
-    // and /etc/hosts
-    virtual void OnDNSChanged() = 0;
-
-   protected:
-    DNSObserver() {}
-
-   private:
-    DISALLOW_COPY_AND_ASSIGN(DNSObserver);
-  };
-
   virtual ~NetworkChangeNotifier();
 
   // See the description of NetworkChangeNotifier::IsOffline().
@@ -105,7 +89,6 @@
   // thread), in which case it will simply do nothing.
   static void AddIPAddressObserver(IPAddressObserver* observer);
   static void AddOnlineStateObserver(OnlineStateObserver* observer);
-  static void AddDNSObserver(DNSObserver* observer);
 
   // Unregisters |observer| from receiving notifications.  This must be called
   // on the same thread on which AddObserver() was called.  Like AddObserver(),
@@ -116,7 +99,6 @@
   // there's no reason to use the API in this risky way, so don't do it.
   static void RemoveIPAddressObserver(IPAddressObserver* observer);
   static void RemoveOnlineStateObserver(OnlineStateObserver* observer);
-  static void RemoveDNSObserver(DNSObserver* observer);
 
   // Allow unit tests to trigger notifications.
   static void NotifyObserversOfIPAddressChangeForTests() {
@@ -131,15 +113,12 @@
   // tests.
   static void NotifyObserversOfIPAddressChange();
   static void NotifyObserversOfOnlineStateChange();
-  static void NotifyObserversOfDNSChange();
 
  private:
   const scoped_refptr<ObserverListThreadSafe<IPAddressObserver> >
       ip_address_observer_list_;
   const scoped_refptr<ObserverListThreadSafe<OnlineStateObserver> >
       online_state_observer_list_;
-  const scoped_refptr<ObserverListThreadSafe<DNSObserver> >
-      resolver_state_observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkChangeNotifier);
 };