third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/src/google/protobuf/util/json_format_proto3.proto

 // 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.
@@ skipping 21 matching lines @@
 
 package proto3;
 
 
 import "google/protobuf/duration.proto";
 import "google/protobuf/timestamp.proto";
 import "google/protobuf/wrappers.proto";
 import "google/protobuf/struct.proto";
 import "google/protobuf/any.proto";
 import "google/protobuf/field_mask.proto";
+import "google/protobuf/unittest.proto";
 
 enum EnumType {
   FOO = 0;
   BAR = 1;
 }
 
 message MessageType {
   int32 value = 1;
 }
 
@@ skipping 115 matching lines @@
 }
 
 message TestBoolValue {
   bool bool_value = 1;
   map<bool, int32> bool_map = 2;
 }
 
 message TestCustomJsonName {
   int32 value = 1 [json_name = "@value"];
 }
+
+message TestExtensions {
+  .protobuf_unittest.TestAllExtensions extensions = 1;
+}