Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/unittest_mset_wire_format.proto

 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
-// http://code.google.com/p/protobuf/
+// 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
@@ skipping 13 matching lines @@
 // 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.
 
 // Author: kenton@google.com (Kenton Varda)
 //  Based on original Protocol Buffers design by
 //  Sanjay Ghemawat, Jeff Dean, and others.
 //
 // This file contains messages for testing message_set_wire_format.
 
-package protobuf_unittest;
+syntax = "proto2";
+package proto2_wireformat_unittest;
 
+option cc_enable_arenas = true;
 option optimize_for = SPEED;
+option csharp_namespace = "Google.ProtocolBuffers.TestProtos";
 
 // A message with message_set_wire_format.
 message TestMessageSet {
   option message_set_wire_format = true;
   extensions 4 to max;
 }
 
-message TestMessageSetContainer {
+message TestMessageSetWireFormatContainer {
   optional TestMessageSet message_set = 1;
 }
-
-message TestMessageSetExtension1 {
-  extend TestMessageSet {
-    optional TestMessageSetExtension1 message_set_extension = 1545008;
-  }
-  optional int32 i = 15;
-}
-
-message TestMessageSetExtension2 {
-  extend TestMessageSet {
-    optional TestMessageSetExtension2 message_set_extension = 1547769;
-  }
-  optional string str = 25;
-}
-
-// MessageSet wire format is equivalent to this.
-message RawMessageSet {
-  repeated group Item = 1 {
-    required int32 type_id = 2;
-    required bytes message = 3;
-  }
-}
-