[net] Add DNS-related signals and NetLog to NetworkChangeNotifier.

net/base/network_change_notifier.cc

Index: net/base/network_change_notifier.cc
diff --git a/net/base/network_change_notifier.cc b/net/base/network_change_notifier.cc
index 593eeeb283b16e09c68f5ffd6d3d28b5e7eec6b4..8f95b13ead60c1aed72e137068fbb985cb8a03d6 100644
--- a/net/base/network_change_notifier.cc
+++ b/net/base/network_change_notifier.cc
@@ -38,6 +38,10 @@ NetworkChangeNotifier::~NetworkChangeNotifier() {
   g_network_change_notifier = NULL;
 }
 
+bool NetworkChangeNotifier::IsCurrentlyWatchingDNS() const {
+  return false;
+}
+
 // static
 void NetworkChangeNotifier::SetFactory(
     NetworkChangeNotifierFactory* factory) {
@@ -76,6 +80,12 @@ bool NetworkChangeNotifier::IsOffline() {
 }
 
 // static
+bool NetworkChangeNotifier::IsWatchingDNS() {
+  return g_network_change_notifier &&
+         g_network_change_notifier->IsCurrentlyWatchingDNS();
+}
+
+// static
 NetworkChangeNotifier* NetworkChangeNotifier::CreateMock() {
   return new MockNetworkChangeNotifier();
 }