Mojo: NULL -> nullptr in mojo/system and mojo/embedder.

mojo/system/dispatcher.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 "mojo/system/dispatcher.h"
 
 #include "base/logging.h"
 #include "mojo/system/constants.h"
 #include "mojo/system/message_pipe_dispatcher.h"
 #include "mojo/system/platform_handle_dispatcher.h"
@@ skipping 464 matching lines @@
 
   return EndSerializeAndCloseImplNoLock(
       channel, destination, actual_size, platform_handles);
 }
 
 // DispatcherTransport ---------------------------------------------------------
 
 void DispatcherTransport::End() {
   DCHECK(dispatcher_);
   dispatcher_->lock_.Release();
-  dispatcher_ = NULL;
+  dispatcher_ = nullptr;
 }
 
 }  // namespace system
 }  // namespace mojo