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

runtime/observatory/tests/service/get_stack_rpc_test.dart

Index: runtime/observatory/tests/service/get_stack_rpc_test.dart
diff --git a/runtime/observatory/tests/service/get_stack_rpc_test.dart b/runtime/observatory/tests/service/get_stack_rpc_test.dart
index 2bf7c3aca56dade158c89727641b854dbf094af5..77578192701d0cfde79d48793da055aaddf27a73 100644
--- a/runtime/observatory/tests/service/get_stack_rpc_test.dart
+++ b/runtime/observatory/tests/service/get_stack_rpc_test.dart
@@ -74,7 +74,7 @@ var tests = [
   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')) {