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

chrome/browser/local_discovery/service_discovery_client_unittest.cc

 // Copyright 2013 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 "base/memory/weak_ptr.h"
 #include "chrome/browser/local_discovery/service_discovery_client_impl.h"
 #include "net/base/net_errors.h"
 #include "net/dns/dns_protocol.h"
 #include "net/dns/mdns_client_impl.h"
 #include "net/dns/mock_mdns_socket_factory.h"
@@ skipping 133 matching lines @@
 };
 
 class ServiceDiscoveryTest : public ::testing::Test {
  public:
   ServiceDiscoveryTest()
       : socket_factory_(new net::MockMDnsSocketFactory),
         mdns_client_(
             scoped_ptr<net::MDnsConnection::SocketFactory>(
                 socket_factory_)) {
     net::MDnsClient::SetInstance(&mdns_client_);
+    mdns_client_.StartListening();
   }
 
   virtual ~ServiceDiscoveryTest() {
     net::MDnsClient::SetInstance(NULL);
   }
 
  protected:
   void RunFor(base::TimeDelta time_period) {
     base::CancelableCallback<void()> callback(base::Bind(
         &ServiceDiscoveryTest::Stop, base::Unretained(this)));
@@ skipping 295 matching lines @@
       ServiceResolver::STATUS_REQUEST_TIMEOUT));
 
   // TODO(noamsml): When NSEC record support is added, change this to use an
   // NSEC record.
   RunFor(base::TimeDelta::FromSeconds(4));
 };
 
 }  // namespace
 
 }  // namespace local_discovery