Send mdns queries for devices on network change

When changing networks, send a new mdns query for devices,
since the device list was flushed.

Review URL: https://codereview.chromium.org/463253002

Cr-Commit-Position: refs/heads/master@{#289230}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289230 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/extensions/api/mdns/dns_sd_registry.cc

@@ -35,11 +35,11 @@ DnsSdRegistry::ServiceTypeData::~ServiceTypeData() {}
 
 void DnsSdRegistry::ServiceTypeData::ListenerAdded() {
   ref_count++;
-};
+}
 
 bool DnsSdRegistry::ServiceTypeData::ListenerRemoved() {
   return --ref_count == 0;
-};
+}
 
 int DnsSdRegistry::ServiceTypeData::GetListenerCount() {
   return ref_count;
@@ -71,7 +71,7 @@ bool DnsSdRegistry::ServiceTypeData::UpdateService(
           << ", known: " << known
           << ", updated or added: " << updated_or_added;
   return updated_or_added;
-};
+}
 
 bool DnsSdRegistry::ServiceTypeData::RemoveService(
     const std::string& service_name) {
@@ -83,9 +83,11 @@ bool DnsSdRegistry::ServiceTypeData::RemoveService(
     }
   }
   return false;
-};
+}
 
 bool DnsSdRegistry::ServiceTypeData::ClearServices() {
+  lister_->Discover(false);
+
   if (service_list_.empty())
     return false;