TaskScheduler: Don't use a callback to post a task from TaskTracker.

base/task_scheduler/task_tracker.h

 // Copyright 2016 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.
 
 #ifndef BASE_TASK_SCHEDULER_TASK_TRACKER_H_
 #define BASE_TASK_SCHEDULER_TASK_TRACKER_H_
 
 #include <memory>
 
 #include "base/base_export.h"
@@ skipping 17 matching lines @@
   ~TaskTracker();
 
   // Synchronously shuts down the scheduler. Once this is called, only tasks
   // posted with the BLOCK_SHUTDOWN behavior will be run. Returns when:
   // - All SKIP_ON_SHUTDOWN tasks that were already running have completed their
   //   execution.
   // - All posted BLOCK_SHUTDOWN tasks have completed their execution.
   // This must only be called once.
   void Shutdown();
 
-  // Posts |task| by calling |post_task_callback| unless the current shutdown
-  // state prevents that. A task forwarded to |post_task_callback| must be
-  // handed back to this instance's RunTask() when it is to be executed.
-  void PostTask(const Callback<void(std::unique_ptr<Task>)>& post_task_callback,
-                std::unique_ptr<Task> task);
+  // Informs this TaskTracker that |task| is about to be posted. Returns true if
+  // this operation is allowed (|task| should be posted if-and-only-if it is).
+  bool WillPostTask(const Task* task);
 
-  // Runs |task| unless the current shutdown state prevents that. |task| must
-  // have been successfully posted via PostTask() first.
+  // Runs |task| unless the current shutdown state prevents that. WillPostTask()
+  // must have allowed |task| to be posted.
   void RunTask(const Task* task);
 
   // Returns true while shutdown is in progress (i.e. Shutdown() has been called
   // but hasn't returned).
   bool IsShuttingDownForTesting() const;
 
   bool shutdown_completed() const {
     AutoSchedulerLock auto_lock(lock_);
     return shutdown_completed_;
   }
 
  private:
-  // Called before a task with |shutdown_behavior| is handed off to
-  // |post_task_callback| by PostTask(). Updates |num_tasks_blocking_shutdown_|
-  // if necessary and returns true if the current shutdown state allows the task
-  // to be posted.
+  // Called before WillPostTask() informs the tracing system that a task has
+  // been posted. Updates |num_tasks_blocking_shutdown_| if necessary and
+  // returns true if the current shutdown state allows the task to be posted.
   bool BeforePostTask(TaskShutdownBehavior shutdown_behavior);
 
   // Called before a task with |shutdown_behavior| is run by RunTask(). Updates
   // |num_tasks_blocking_shutdown_| if necessary and returns true if the current
   // shutdown state allows the task to be run.
   bool BeforeRunTask(TaskShutdownBehavior shutdown_behavior);
 
   // Called after a task with |shutdown_behavior| has been run by RunTask().
   // Updates |num_tasks_blocking_shutdown_| and signals |shutdown_cv_| if
   // necessary.
@@ skipping 15 matching lines @@
   // True once Shutdown() has returned. No new task can be scheduled after this.
   bool shutdown_completed_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(TaskTracker);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_TRACKER_H_