Introduce debug events for Microtask queue.

src/object-observe.js

 // Copyright 2012 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.
 
 "use strict";
 
 // Overview:
 //
 // This file contains all of the routing and accounting for Object.observe.
 // User code will interact with these mechanisms via the Object.observe APIs
@@ skipping 27 matching lines @@
 function GetObservationStateJS() {
   if (IS_UNDEFINED(observationState))
     observationState = %GetObservationState();
 
   if (IS_UNDEFINED(observationState.callbackInfoMap)) {
     observationState.callbackInfoMap = %ObservationWeakMapCreate();
     observationState.objectInfoMap = %ObservationWeakMapCreate();
     observationState.notifierObjectInfoMap = %ObservationWeakMapCreate();
     observationState.pendingObservers = null;
     observationState.nextCallbackPriority = 0;
+    observationState.lastMicrotaskId = 0;
   }
 
   return observationState;
 }
 
 function GetWeakMapWrapper() {
   function MapWrapper(map) {
     this.map_ = map;
   };
 
@@ skipping 356 matching lines @@
 
   var callback = ObserverGetCallback(observer);
   if (!%ObserverObjectAndRecordHaveSameOrigin(callback, changeRecord.object,
                                               changeRecord)) {
     return;
   }
 
   var callbackInfo = CallbackInfoNormalize(callback);
   if (IS_NULL(GetPendingObservers())) {
     SetPendingObservers(nullProtoObject());
-    %EnqueueMicrotask(ObserveMicrotaskRunner);
+    if (DEBUG_IS_ACTIVE) {
+      var id = ++GetObservationStateJS().lastMicrotaskId;
+      var name = "Object.observe";
+      %EnqueueMicrotask(function() {
+        %DebugAsyncTaskEvent({ type: "willHandle", id: id, name: name });
+        ObserveMicrotaskRunner();
+        %DebugAsyncTaskEvent({ type: "didHandle", id: id, name: name });
+      });
+      %DebugAsyncTaskEvent({ type: "enqueue", id: id, name: name });
+    } else {
+      %EnqueueMicrotask(ObserveMicrotaskRunner);
+    }
   }
   GetPendingObservers()[callbackInfo.priority] = callback;
   callbackInfo.push(changeRecord);
 }
 
 function ObjectInfoEnqueueExternalChangeRecord(objectInfo, changeRecord, type) {
   if (!ObjectInfoHasActiveObservers(objectInfo))
     return;
 
   var hasType = !IS_UNDEFINED(type);
@@ skipping 196 matching lines @@
     "observe", ArrayObserve,
     "unobserve", ArrayUnobserve
   ));
   InstallFunctions(notifierPrototype, DONT_ENUM, $Array(
     "notify", ObjectNotifierNotify,
     "performChange", ObjectNotifierPerformChange
   ));
 }
 
 SetupObjectObserve();