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

net/base/host_resolver_impl.h

Index: net/base/host_resolver_impl.h
===================================================================
--- net/base/host_resolver_impl.h	(revision 99676)
+++ net/base/host_resolver_impl.h	(working copy)
@@ -62,8 +62,7 @@
 class NET_EXPORT HostResolverImpl
     : public HostResolver,
       NON_EXPORTED_BASE(public base::NonThreadSafe),
-      public NetworkChangeNotifier::IPAddressObserver,
-      public NetworkChangeNotifier::DNSObserver {
+      public NetworkChangeNotifier::IPAddressObserver {
  public:
   // The index into |job_pools_| for the various job pools. Pools with a higher
   // index have lower priority.
@@ -305,9 +304,6 @@
     retry_factor_ = retry_factor;
   }
 
-  // NetworkChangeNotifier::OnDNSChanged methods:
-  virtual void OnDNSChanged();
-
   // Cache of host resolution results.
   scoped_ptr<HostCache> cache_;