Track async causal stack traces

tests/standalone/dart_developer_disabled_env_test.dart

Index: tests/standalone/dart_developer_disabled_env_test.dart
diff --git a/tests/standalone/dart_developer_disabled_env_test.dart b/tests/standalone/dart_developer_disabled_env_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1d9653baa416135411786edda9b9b1d686d6cf21
--- /dev/null
+++ b/tests/standalone/dart_developer_disabled_env_test.dart
@@ -0,0 +1,11 @@
+// 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=--no_causal_async_stacks
+
+import "package:expect/expect.dart";
+
+main() {
+  Expect.isFalse(
+      const bool.fromEnvironment('dart.developer.causal_async_stacks'));
+}