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

base/task_scheduler/task_tracker.cc

Index: base/task_scheduler/task_tracker.cc
diff --git a/base/task_scheduler/task_tracker.cc b/base/task_scheduler/task_tracker.cc
index 50922bbc8cf9004491bc59c1ac4d6bdbf3e1c5d3..c896a9fad9b4f517f0f78499d4df31052668a14a 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -58,19 +58,16 @@ void TaskTracker::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) {