Adds a special case for sending an int over a port with the native API.

runtime/observatory/tests/service/get_stack_rpc_test.dart

 // Copyright (c) 2015, 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.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'dart:async';
 import 'dart:isolate' as isolate;
@@ skipping 56 matching lines @@
   // Sanity check.
   expect(stack['messages'].length, greaterThanOrEqualTo(1));
 
   // Iterate over messages.
   var messageDepth = 0;
   // objectId of message to be handled by msgHandler.
   var msgHandlerObjectId;
   for (var message in stack['messages']) {
     print('checking message $messageDepth');
     expect(message.index, equals(messageDepth++));
-    expect(message.size, greaterThanOrEqualTo(1));
+    expect(message.size, greaterThanOrEqualTo(0));
     expect(message.handler.type, equals('Function'));
     expect(message.location.type, equals('SourceLocation'));
     if (message.handler.name.contains('msgHandler')) {
       msgHandlerObjectId = message.messageObjectId;
     }
   }
   expect(msgHandlerObjectId, isNotNull);
 
   // Get object.
   var object = await isolate.getObject(msgHandlerObjectId);
   expect(object.valueAsString, equals('34'));
 }
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: startTimer);