Rewrite CancelableTaskTracker unit tests

chrome/common/cancelable_task_tracker.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // CancelableTaskTracker posts tasks (in the form of a Closure) to a TaskRunner,
 // and is able to cancel the task later if it's not needed anymore. On
 // destruction, CancelableTaskTracker will cancel all tracked tasks.
 //
 // Each cancelable task can be associated with a reply (also a Closure). After
 // the task is run on the TaskRunner, |reply| will be posted back to originating
@@ skipping 55 matching lines @@
                   const tracked_objects::Location& from_here,
                   const base::Closure& task);
 
   TaskId PostTaskAndReply(base::TaskRunner* task_runner,
                           const tracked_objects::Location& from_here,
                           const base::Closure& task,
                           const base::Closure& reply);
 
   // Creates a tracked TaskId and an associated IsCanceledCallback. Client can
   // later call TryCancel() with the returned TaskId, and run |is_canceled_cb|
-  // to check whether the TaskId is canceled.
+  // from any thread to check whether the TaskId is canceled.
   //
   // Note. This function is used to address some special cancelation requirement
   // in existing code. You SHOULD NOT need this function in new code.
   TaskId NewTrackedTaskId(IsCanceledCallback* is_canceled_cb);
 
   // After calling this function, |task| and |reply| will not run. If the
   // cancelation happens when |task| is running or has finished running, |reply|
   // will not run. If |reply| is running or has finished running, cancellation
   // is a noop.
   //
@@ skipping 12 matching lines @@
   base::hash_map<TaskId, base::CancellationFlag*> task_flags_;
   base::WeakPtrFactory<CancelableTaskTracker> weak_factory_;
 
   TaskId next_id_;
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(CancelableTaskTracker);
 };
 
 #endif  // CHROME_COMMON_CANCELABLE_TASK_TRACKER_H_