third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.cs

 #region Copyright notice and license
 // Protocol Buffers - Google's data interchange format
 // Copyright 2015 Google Inc.  All rights reserved.
 // https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
@@ skipping 703 matching lines @@
         [Test]
         public void CustomDiagnosticMessage_DirectToTextWriterCall()
         {
             var message = new ForeignMessage { C = 31 };
             var writer = new StringWriter();
             JsonFormatter.Default.Format(message, writer);
             Assert.AreEqual("{ \"c\": 31 }", writer.ToString());
         }
     }
 }