Update //third_party/protobuf to version 3.

third_party/protobuf/python/google/protobuf/internal/more_messages.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
 // 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.
 
 // Author: robinson@google.com (Will Robinson)
 
+syntax = "proto2";
 
 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;
 }