Avoid to mask all the NetworkRpcException

runtime/observatory/tests/service/test_helper.dart

Index: runtime/observatory/tests/service/test_helper.dart
diff --git a/runtime/observatory/tests/service/test_helper.dart b/runtime/observatory/tests/service/test_helper.dart
index 1d2ea9d54dec24b1ab974940b3970138cb865a76..0b7749e1b39cc6f7eac493874c211e33d64c1f7f 100644
--- a/runtime/observatory/tests/service/test_helper.dart
+++ b/runtime/observatory/tests/service/test_helper.dart
@@ -310,7 +310,10 @@ class _ServiceTesterRunner {
         await process.requestExit();
       }, onError: (e, st) {
         process.requestExit();
-        if (!_isWebSocketDisconnect(e)) {
+        // TODO: remove this workaround.

[Cutch, 2016/06/23 17:59:20]

Can you please expand on this comment and explain why checking for a non-null
stacktrace works around the issue?

[cbernaschina, 2016/06/23 18:27:24]

Done.

+        // This is necessary due to non awaited operations.
+        // E.G. object.dart (398~402)
+        if (st != null || !_isWebSocketDisconnect(e)) {
           print('Unexpected exception in service tests: $e $st');
           throw e;
         }