Avoid to mask all the NetworkRpcException

runtime/observatory/tests/service/test_helper.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 test_helper;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'package:observatory/service_io.dart';
@@ skipping 292 matching lines @@
             vm.verbose = verbose_vm;
             print('Running $name [$testIndex/$totalTests]');
             testIndex++;
             await test(isolate);
           }
         }
 
         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;
         }
       });
     });
   }
 }
 
 /// Runs [tests] in sequence, each of which should take an [Isolate] and
 /// return a [Future]. Code for setting up state can run before and/or
@@ skipping 91 matching lines @@
         mainArgs: mainArgs,
         vmTests: tests,
         pause_on_start: pause_on_start,
         pause_on_exit: pause_on_exit,
         trace_service: trace_service,
         trace_compiler: trace_compiler,
         verbose_vm: verbose_vm,
         pause_on_unhandled_exceptions: pause_on_unhandled_exceptions);
   }
 }