Revert of Redirect the MessageLoop's task runner to the renderer scheduler

components/scheduler/child/scheduler_helper.cc

 // Copyright 2015 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 "components/scheduler/child/scheduler_helper.h"
 
 #include "base/time/default_tick_clock.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
-#include "components/scheduler/child/scheduler_task_runner_delegate.h"
+#include "components/scheduler/child/nestable_single_thread_task_runner.h"
 
 namespace scheduler {
 
 SchedulerHelper::SchedulerHelper(
-    scoped_refptr<SchedulerTaskRunnerDelegate> main_task_runner,
+    scoped_refptr<NestableSingleThreadTaskRunner> main_task_runner,
     const char* tracing_category,
     const char* disabled_by_default_tracing_category,
     const char* disabled_by_default_verbose_tracing_category,
     size_t total_task_queue_count)
-    : main_task_runner_(main_task_runner),
-      task_queue_selector_(new PrioritizingTaskQueueSelector()),
+    : task_queue_selector_(new PrioritizingTaskQueueSelector()),
       task_queue_manager_(
           new TaskQueueManager(total_task_queue_count,
                                main_task_runner,
                                task_queue_selector_.get(),
                                disabled_by_default_tracing_category,
                                disabled_by_default_verbose_tracing_category)),
       quiescence_monitored_task_queue_mask_(
           ((1ull << total_task_queue_count) - 1ull) &
           ~(1ull << QueueId::CONTROL_TASK_QUEUE) &
           ~(1ull << QueueId::CONTROL_TASK_AFTER_WAKEUP_QUEUE)),
@@ skipping 26 matching lines @@
       QueueId::CONTROL_TASK_AFTER_WAKEUP_QUEUE,
       TaskQueueManager::WakeupPolicy::DONT_WAKE_OTHER_QUEUES);
 
   for (size_t i = 0; i < TASK_QUEUE_COUNT; i++) {
     task_queue_manager_->SetQueueName(
         i, TaskQueueIdToString(static_cast<QueueId>(i)));
   }
 
   // TODO(skyostil): Increase this to 4 (crbug.com/444764).
   task_queue_manager_->SetWorkBatchSize(1);
-
-  main_task_runner_->SetDefaultTaskRunner(
-      task_queue_manager_->TaskRunnerForQueue(QueueId::DEFAULT_TASK_QUEUE));
 }
 
 SchedulerHelper::~SchedulerHelper() {
-  Shutdown();
 }
 
 void SchedulerHelper::Shutdown() {
   CheckOnValidThread();
   task_queue_manager_.reset();
-  main_task_runner_->RestoreDefaultTaskRunner();
 }
 
 scoped_refptr<base::SingleThreadTaskRunner>
 SchedulerHelper::DefaultTaskRunner() {
   CheckOnValidThread();
   return default_task_runner_;
 }
 
 scoped_refptr<base::SingleThreadTaskRunner>
 SchedulerHelper::ControlTaskRunner() {
@@ skipping 127 matching lines @@
 }
 
 void SchedulerHelper::RemoveTaskObserver(
     base::MessageLoop::TaskObserver* task_observer) {
   CheckOnValidThread();
   if (task_queue_manager_)
     task_queue_manager_->RemoveTaskObserver(task_observer);
 }
 
 }  // namespace scheduler