Revert "third_party/protobuf: Update to HEAD (5f65ee6ac7)"

third_party/protobuf/csharp/src/Google.Protobuf/CodedInputStream.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 594 matching lines @@
 
         /// <summary>
         /// Reads a uint32 field value from the stream.
         /// </summary>   
         public uint ReadUInt32()
         {
             return ReadRawVarint32();
         }
 
         /// <summary>
-        /// Reads an enum field value from the stream.
+        /// Reads an enum field value from the stream. If the enum is valid for type T,
+        /// then the ref value is set and it returns true.  Otherwise the unknown output
+        /// value is set and this method returns false.
         /// </summary>   
         public int ReadEnum()
         {
             // Currently just a pass-through, but it's nice to separate it logically from WriteInt32.
             return (int) ReadRawVarint32();
         }
 
         /// <summary>
         /// Reads an sfixed32 field value from the stream.
         /// </summary>   
@@ skipping 640 matching lines @@
                         throw InvalidProtocolBufferException.TruncatedMessage();
                     }
                     amountToSkip -= bytesRead;
                 }
             }
         }
 
         #endregion
     }
 }