third_party/protobuf: Update to HEAD (83d681ee2c)

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

 #region Copyright notice and license
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 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 399 matching lines @@
             using (var cos = new CodedOutputStream(memoryStream, true))
             {
                 cos.WriteRawByte(0);
                 Assert.AreEqual(0, memoryStream.Position); // Not flushed yet
             }
             Assert.AreEqual(1, memoryStream.Position); // Flushed data from CodedOutputStream to MemoryStream
             Assert.IsTrue(memoryStream.CanWrite); // We left the stream open
         }
     }
 }