replace NULL->nullptr in src/remoting.

remoting/host/register_support_host_request.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 "remoting/host/register_support_host_request.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 158 matching lines @@
   bool success = ParseResponse(response, &support_id, &lifetime);
   CallCallback(success, support_id, lifetime);
 }
 
 void RegisterSupportHostRequest::CallCallback(
     bool success, const std::string& support_id, base::TimeDelta lifetime) {
   // Cleanup state before calling the callback.
   request_.reset();
   iq_sender_.reset();
   signal_strategy_->RemoveListener(this);
-  signal_strategy_ = NULL;
+  signal_strategy_ = nullptr;
 
   RegisterCallback callback = callback_;
   callback_.Reset();
   callback.Run(success, support_id, lifetime);
 }
 
 }  // namespace remoting