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

runtime/observatory/tests/service/get_isolate_after_async_error_test.dart

Index: runtime/observatory/tests/service/get_isolate_after_async_error_test.dart
diff --git a/runtime/observatory/tests/service/get_isolate_after_async_error_test.dart b/runtime/observatory/tests/service/get_isolate_after_async_error_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..a0c531d16e0c5114dc22cb86424b2fe75116ed06
--- /dev/null
+++ b/runtime/observatory/tests/service/get_isolate_after_async_error_test.dart
@@ -0,0 +1,28 @@
+// 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 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'test_helper.dart';
+import 'service_test_common.dart';
+
+doThrow() async {
+  throw "oh no"; // Line 13.
+}
+
+var tests = [
+  hasStoppedAtExit,
+
+  (Isolate isolate) async {
+    await isolate.reload();
+    expect(isolate.error, isNotNull);
+    expect(isolate.error.message.contains('oh no'), isTrue);
+  }
+];
+
+main(args) async => runIsolateTests(args,
+                                    tests,
+                                    pause_on_exit: true,
+                                    testeeConcurrent: doThrow);