[net/dns] Isolate DnsConfigWatcher from DnsConfigService.

net/dns/dns_config_service.cc

 // 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.
 
 #include "net/dns/dns_config_service.h"
 
 #include "base/logging.h"
 #include "base/values.h"
 #include "net/base/ip_endpoint.h"
 
@@ skipping 59 matching lines @@
 
   return dict;
 }
 
 
 DnsConfigService::DnsConfigService()
     : have_config_(false),
       have_hosts_(false),
       need_update_(false) {}
 
-DnsConfigService::~DnsConfigService() {}
+DnsConfigService::~DnsConfigService() {
+  // Must always clean up.
+  NetworkChangeNotifier::RemoveDNSObserver(this);
+}
+
+void DnsConfigService::Read(const CallbackType& callback) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(!callback.is_null());
+  DCHECK(callback_.is_null());
+  callback_ = callback;
+  OnDNSChanged(NetworkChangeNotifier::CHANGE_DNS_WATCH_STARTED);
+}
+
+void DnsConfigService::Watch(const CallbackType& callback) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(!callback.is_null());
+  DCHECK(callback_.is_null());
+  NetworkChangeNotifier::AddDNSObserver(this);
+  callback_ = callback;
+  if (NetworkChangeNotifier::IsWatchingDNS())
+    OnDNSChanged(NetworkChangeNotifier::CHANGE_DNS_WATCH_STARTED);
+  // else: Wait until signal before reading.
+}
 
 void DnsConfigService::InvalidateConfig() {
   DCHECK(CalledOnValidThread());
   if (!have_config_)
     return;
   have_config_ = false;
   StartTimer();
 }
 
 void DnsConfigService::InvalidateHosts() {
@@ skipping 64 matching lines @@
 void DnsConfigService::OnCompleteConfig() {
   timer_.Stop();
   if (need_update_) {
     need_update_ = false;
     callback_.Run(dns_config_);
   }
 }
 
 }  // namespace net