Detect unhandled exceptions in async functions without an awaiter

runtime/observatory/tests/service/awaiter_async_stack_contents_test.dart

Index: runtime/observatory/tests/service/awaiter_async_stack_contents_test.dart
diff --git a/runtime/observatory/tests/service/awaiter_async_stack_contents_test.dart b/runtime/observatory/tests/service/awaiter_async_stack_contents_test.dart
index a572cb1926216ed2808f80c4dd54835843f85df3..d5a66868609e183e31f64bace2fd9a332910a02d 100644
--- a/runtime/observatory/tests/service/awaiter_async_stack_contents_test.dart
+++ b/runtime/observatory/tests/service/awaiter_async_stack_contents_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2017, 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  --verbose_debug
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
 import 'dart:developer';
 import 'package:observatory/models.dart' as M;
@@ -41,11 +41,6 @@ var tests = [
   resumeIsolate,
   hasStoppedAtBreakpoint,
   stoppedAtLine(LINE_A),
-  (Isolate isolate) async {
-    ServiceMap stack = await isolate.getStack();
-    // No awaiter frames because there is no awaiter.
-    expect(stack['awaiterFrames'], isNull);
-  },
   resumeIsolate,
   hasStoppedAtBreakpoint,
   stoppedAtLine(LINE_C),