TaskScheduler: Make the worker pools of TaskSchedulerImpl configurable

base/task_scheduler/task_scheduler.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_scheduler.h"
 
 #include "base/logging.h"
-#include "base/task_scheduler/task_scheduler_impl.h"
 
 namespace base {
 
 namespace {
 
 // |g_task_scheduler| is intentionally leaked on shutdown.
 TaskScheduler* g_task_scheduler = nullptr;
 
 }  // namespace
 
 // static
 void TaskScheduler::SetInstance(std::unique_ptr<TaskScheduler> task_scheduler) {
   delete g_task_scheduler;
   g_task_scheduler = task_scheduler.release();
 }
 
 // static
-void TaskScheduler::InitializeDefaultTaskScheduler() {
-  SetInstance(internal::TaskSchedulerImpl::Create());
-}
-
-// static
 TaskScheduler* TaskScheduler::GetInstance() {
   return g_task_scheduler;
 }
 
 }  // namespace base