Maintaing the proper order of initialization WeakPtrFactory

base/task/cancelable_task_tracker.h

 // Copyright 2014 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
@@ skipping 108 matching lines @@
 
   // Returns true iff there are in-flight tasks that are still being
   // tracked.
   bool HasTrackedTasks() const;
 
  private:
   void Track(TaskId id, base::CancellationFlag* flag);
   void Untrack(TaskId id);
 
   base::hash_map<TaskId, base::CancellationFlag*> task_flags_;
-  base::WeakPtrFactory<CancelableTaskTracker> weak_factory_;
 
   TaskId next_id_;
   base::ThreadChecker thread_checker_;
 
+  base::WeakPtrFactory<CancelableTaskTracker> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(CancelableTaskTracker);
 };
 
 }  // namespace base
 
 #endif  // BASE_TASK_CANCELABLE_TASK_TRACKER_H_