Revert 99677 (didn't help) - Revert 99666 (sync tests started failing on mac10.6:

net/base/host_resolver_impl.cc

Index: net/base/host_resolver_impl.cc
===================================================================
--- net/base/host_resolver_impl.cc	(revision 99692)
+++ net/base/host_resolver_impl.cc	(working copy)
@@ -30,6 +30,7 @@
 #include "base/values.h"
 #include "net/base/address_list.h"
 #include "net/base/address_list_net_log_param.h"
+#include "net/base/dns_reloader.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/host_resolver_proc.h"
 #include "net/base/net_errors.h"
@@ -1090,6 +1091,10 @@
     additional_resolver_flags_ |= HOST_RESOLVER_LOOPBACK_ONLY;
 #endif
   NetworkChangeNotifier::AddIPAddressObserver(this);
+#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
+  EnsureDnsReloaderInit();
+  NetworkChangeNotifier::AddDNSObserver(this);
+#endif
 }
 
 HostResolverImpl::~HostResolverImpl() {
@@ -1104,6 +1109,9 @@
     cur_completing_job_->Cancel();
 
   NetworkChangeNotifier::RemoveIPAddressObserver(this);
+#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
+  NetworkChangeNotifier::RemoveDNSObserver(this);
+#endif
 
   // Delete the job pools.
   for (size_t i = 0u; i < arraysize(job_pools_); ++i)
@@ -1644,4 +1652,17 @@
   // |this| may be deleted inside AbortAllInProgressJobs().
 }
 
+void HostResolverImpl::OnDNSChanged() {
+  // If the DNS server has changed, existing cached info could be wrong so we
+  // have to drop our internal cache :( Note that OS level DNS caches, such
+  // as NSCD's cache should be dropped automatically by the OS when
+  // resolv.conf changes so we don't need to do anything to clear that cache.
+  if (cache_.get())
+    cache_->clear();
+  // Existing jobs will have been sent to the original server so they need to
+  // be aborted. TODO(Craig): Should these jobs be restarted?
+  AbortAllInProgressJobs();
+  // |this| may be deleted inside AbortAllInProgressJobs().
+}
+
 }  // namespace net