Track async causal stack traces

runtime/observatory/tests/service/causal_async_stack_presence_test.dart

+// 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
+
+import 'dart:developer';
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'service_test_common.dart';
+import 'test_helper.dart';
+
+const LINE_C = 18;
+const LINE_A = 23;
+const LINE_B = 29;
+
+foobar() {
+  debugger();
+  print('foobar');  // LINE_C.
+}
+
+helper() async {
+  debugger();
+  print('helper');  // LINE_A.
+  foobar();
+}
+
+testMain() {
+  debugger();
+  helper();  // LINE_B.
+}
+
+var tests = [
+  hasStoppedAtBreakpoint,
+  stoppedAtLine(LINE_B),
+  (Isolate isolate) async {
+    ServiceMap stack = await isolate.getStack();
+    // No causal frames because we are in a completely synchronous stack.
+    expect(stack['asyncCausalFrames'], isNull);
+  },
+  resumeIsolate,
+  hasStoppedAtBreakpoint,
+  stoppedAtLine(LINE_A),
+
+  (Isolate isolate) async {
+    ServiceMap stack = await isolate.getStack();
+    // Has causal frames (we are inside an async function)
+    expect(stack['asyncCausalFrames'], isNotNull);
+  },
+
+  resumeIsolate,
+  hasStoppedAtBreakpoint,
+  stoppedAtLine(LINE_C),
+
+  (Isolate isolate) async {
+    ServiceMap stack = await isolate.getStack();
+    // Has causal frames (we are inside a function called by an async function)
+    expect(stack['asyncCausalFrames'], isNotNull);
+  },
+];
+
+main(args) => runIsolateTestsSynchronous(args,
+                                         tests,
+                                         testeeConcurrent: testMain);