Introduce debug events for Microtask queue.

test/mjsunit/es6/debug-promises-async-task-event.js

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --expose-debug-as debug
+
+Debug = debug.Debug;
+
+var base_id = -1;
+var exception = null;
+var expected = [
+  "enqueue #1",
+  "willHandle #1",
+  "then #1",
+  "enqueue #2",
+  "didHandle #1",
+  "willHandle #2",
+  "then #2",
+  "enqueue #3",
+  "didHandle #2",
+  "willHandle #3",
+  "didHandle #3"
+];
+
+function assertLog(msg)
+{
+  print(msg);
+  assertTrue(expected.length > 0);
+  assertEquals(expected.shift(), msg);
+  if (!expected.length) {
+    Debug.setListener(null);
+  }
+}
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.AsyncTaskEvent) return;
+  try {
+    if (base_id < 0)
+      base_id = event_data.id();
+    var id = event_data.id() - base_id + 1;
+    assertEquals("Promise.Resolved", event_data.name());
+    assertLog(event_data.type() + " #" + id);
+  } catch (e) {
+    print(e + e.stack)
+    exception = e;
+  }
+}
+
+Debug.setListener(listener);
+
+var resolver;
+var p = new Promise(function(resolve, reject) {
+  resolver = resolve;
+});
+p.then(function() {
+  assertLog("then #1");
+}).then(function() {
+  assertLog("then #2");
+});
+resolver();
+
+assertNull(exception);