Add test for protocol buffer hash code

test/all_tests.dart

 #!/usr/bin/env dart
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library protoc_plugin_all_tests;
 
 import 'enum_generator_test.dart' as egt;
 import 'generated_message_test.dart' as gmt;
 import 'indenting_writer_test.dart' as iwt;
 import 'json_test.dart' as jt;
 import 'message_generator_test.dart' as mgt;
 import 'file_generator_test.dart' as fgt;
 import 'message_test.dart' as mt;
 import 'protoc_options_test.dart' as pot;
 import 'unknown_field_set_test.dart' as ufst;
 import 'validate_fail_test.dart' as vft;
 import 'wire_format_test.dart' as wft;
 import 'reserved_names_test.dart' as rnt;
+import 'hash_code_test.dart' as hct;
 
 void main() {
   egt.main();
   gmt.main();
   iwt.main();
   jt.main();
   mgt.main();
   fgt.main();
   mt.main();
   pot.main();
   ufst.main();
   vft.main();
   wft.main();
   rnt.main();
+  hct.main();
 }