Update //third_party/protobuf to version 3.

third_party/protobuf/csharp/src/Google.Protobuf/IDeepCloneable.cs

+#region Copyright notice and license
 // Protocol Buffers - Google's data interchange format
-// Copyright 2008 Google Inc.  All rights reserved.
-// http://code.google.com/p/protobuf/
+// 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
 // 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
 
-// Author: robinson@google.com (Will Robinson)
-
-
-package google.protobuf.internal;
-
-// A message where tag numbers are listed out of order, to allow us to test our
-// canonicalization of serialized output, which should always be in tag order.
-// We also mix in some extensions for extra fun.
-message OutOfOrderFields {
-  optional   sint32 optional_sint32   =  5;
-  extensions 4 to 4;
-  optional   uint32 optional_uint32   =  3;
-  extensions 2 to 2;
-  optional    int32 optional_int32    =  1;
-};
-
-
-extend OutOfOrderFields {
-  optional   uint64 optional_uint64   =  4;
-  optional    int64 optional_int64    =  2;
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Generic interface for a deeply cloneable type.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// All generated messages implement this interface, but so do some non-message types.
+    /// Additionally, due to the type constraint on <c>T</c> in <see cref="IMessage{T}"/>,
+    /// it is simpler to keep this as a separate interface.
+    /// </para>
+    /// </remarks>
+    /// <typeparam name="T">The type itself, returned by the <see cref="Clone"/> method.</typeparam>
+    public interface IDeepCloneable<T>
+    {
+        /// <summary>
+        /// Creates a deep clone of this object.
+        /// </summary>
+        /// <returns>A deep clone of this object.</returns>
+        T Clone();
+    }
 }