Revert https://codereview.chromium.org/1291903002 (protobuf roll).

third_party/protobuf/csharp/src/Google.Protobuf/IMessage.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
-// notice, this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above
-// copyright notice, this list of conditions and the following disclaimer
-// in the documentation and/or other materials provided with the
-// distribution.
-//     * Neither the name of Google Inc. nor the names of its
-// contributors may be used to endorse or promote products derived from
-// this software without specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-#endregion
-
-using System;
-using Google.Protobuf.Reflection;
-
-namespace Google.Protobuf
-{
-    /// <summary>
-    /// Interface for a Protocol Buffers message, supporting
-    /// basic operations required for serialization.
-    /// </summary>
-    public interface IMessage
-    {
-        /// <summary>
-        /// Merges the data from the specified coded input stream with the current message.
-        /// </summary>
-        /// <remarks>See the user guide for precise merge semantics.</remarks>
-        /// <param name="input"></param>
-        void MergeFrom(CodedInputStream input);
-
-        /// <summary>
-        /// Writes the data to the given coded output stream.
-        /// </summary>
-        /// <param name="output">Coded output stream to write the data to. Must not be null.</param>
-        void WriteTo(CodedOutputStream output);
-
-        /// <summary>
-        /// Calculates the size of this message in Protocol Buffer wire format, in bytes.
-        /// </summary>
-        /// <returns>The number of bytes required to write this message
-        /// to a coded output stream.</returns>
-        int CalculateSize();
-
-        /// <summary>
-        /// Descriptor for this message. All instances are expected to return the same descriptor,
-        /// and for generated types this will be an explicitly-implemented member, returning the
-        /// same value as the static property declared on the type.
-        /// </summary>
-        MessageDescriptor Descriptor { get; }
-    }
-
-    /// <summary>
-    /// Generic interface for a Protocol Buffers message,
-    /// where the type parameter is expected to be the same type as
-    /// the implementation class.
-    /// </summary>
-    /// <typeparam name="T">The message type.</typeparam>
-    public interface IMessage<T> : IMessage, IEquatable<T>, IDeepCloneable<T> where T : IMessage<T>
-    {
-        /// <summary>
-        /// Merges the given message into this one.
-        /// </summary>
-        /// <remarks>See the user guide for precise merge semantics.</remarks>
-        /// <param name="message">The message to merge with this one. Must not be null.</param>
-        void MergeFrom(T message);
-    }
-}