Add heart beat tests to make sure we see an isolate's sticky error after exit

runtime/observatory/tests/service/get_isolate_after_language_error_test.dart

Index: runtime/observatory/tests/service/get_isolate_after_language_error_test.dart
diff --git a/runtime/observatory/tests/service/pause_on_unhandled_exceptions_test.dart b/runtime/observatory/tests/service/get_isolate_after_language_error_test.dart
similarity index 60%
copy from runtime/observatory/tests/service/pause_on_unhandled_exceptions_test.dart
copy to runtime/observatory/tests/service/get_isolate_after_language_error_test.dart
index 2e09acc5d5073a9917f10376beb66dcb1f886db9..dc763a00d8f10e92dd8d9d53fb46ac9839c9cb24 100644
--- a/runtime/observatory/tests/service/pause_on_unhandled_exceptions_test.dart
+++ b/runtime/observatory/tests/service/get_isolate_after_language_error_test.dart
@@ -1,29 +1,32 @@
-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2016, 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 'dart:async';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'service_test_common.dart';
 
+var x;
+
 doThrow() {
-  throw "TheException"; // Line 13.
-  return "end of doThrow";
+  if (x) while {
+  };
 }
 
 var tests = [
-  hasStoppedWithUnhandledException,
+  hasStoppedAtExit,
 
   (Isolate isolate) async {
-    print("We stoppped!");
-    var stack = await isolate.getStack();
-    expect(stack['frames'][0].function.name, equals('doThrow'));
+    await isolate.reload();
+    expect(isolate.error, isNotNull);
+    expect(isolate.error.message.contains("'(' expected"), isTrue);
   }
 ];
 
 main(args) => runIsolateTestsSynchronous(args,
                                          tests,
-                                         pause_on_unhandled_exceptions: true,
-                                         testeeConcurrent: doThrow);
+                                         pause_on_exit: true,
+                                         testeeConcurrent: doThrow);