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

base/task_scheduler/task_tracker.cc

 // 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.
 
 #include "base/task_scheduler/task_tracker.h"
 
 #include "base/callback.h"
 #include "base/debug/task_annotator.h"
 #include "base/metrics/histogram_macros.h"
 
@@ skipping 40 matching lines @@
   // than |kMaxBlockShutdownTasksPostedDuringShutdown| BLOCK_SHUTDOWN tasks were
   // posted during shutdown. Otherwise, the histogram has already been recorded
   // in BeforePostTask().
   if (num_block_shutdown_tasks_posted_during_shutdown_ <
       kMaxBlockShutdownTasksPostedDuringShutdown) {
     RecordNumBlockShutdownTasksPostedDuringShutdown(
         num_block_shutdown_tasks_posted_during_shutdown_);
   }
 }
 
-void TaskTracker::PostTask(
-    const Callback<void(std::unique_ptr<Task>)>& post_task_callback,
-    std::unique_ptr<Task> task) {
-  DCHECK(!post_task_callback.is_null());
+bool TaskTracker::WillPostTask(const Task* task) {
   DCHECK(task);
 
   if (!BeforePostTask(task->traits.shutdown_behavior()))
-    return;
+    return false;
 
   debug::TaskAnnotator task_annotator;
   task_annotator.DidQueueTask(kQueueFunctionName, *task);
 
-  post_task_callback.Run(std::move(task));
+  return true;
 }
 
 void TaskTracker::RunTask(const Task* task) {
   DCHECK(task);
 
   const TaskShutdownBehavior shutdown_behavior =
       task->traits.shutdown_behavior();
   if (!BeforeRunTask(shutdown_behavior))
     return;
 
@@ skipping 90 matching lines @@
     AutoSchedulerLock auto_lock(lock_);
     DCHECK_GT(num_tasks_blocking_shutdown_, 0U);
     --num_tasks_blocking_shutdown_;
     if (num_tasks_blocking_shutdown_ == 0 && shutdown_cv_)
       shutdown_cv_->Signal();
   }
 }
 
 }  // namespace internal
 }  // namespace base