Add an explicit way of forcing the MDnsClient to listen on the network

net/dns/mdns_client.h

Index: net/dns/mdns_client.h
diff --git a/net/dns/mdns_client.h b/net/dns/mdns_client.h
index 9e3bdb75302a544adef9693912ef6e41dc829433..21022c8355b99704133627321cf72ea3cf82a43f 100644
--- a/net/dns/mdns_client.h
+++ b/net/dns/mdns_client.h
@@ -143,6 +143,13 @@ class NET_EXPORT MDnsClient {
       int flags,
       const MDnsTransaction::ResultCallback& callback) = 0;
 
+  virtual bool StartListening() = 0;
+
+  // Do not call this inside callbacks from related MDnsListener and
+  // MDnsTransaction objects.
+  virtual void StopListening() = 0;
+  virtual bool IsListening() const = 0;
+
   // Lazily create and return static instance for MDnsClient.
   static MDnsClient* GetInstance();