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

components/scheduler/child/scheduler_helper.h

Index: components/scheduler/child/scheduler_helper.h
diff --git a/components/scheduler/child/scheduler_helper.h b/components/scheduler/child/scheduler_helper.h
index 5b3c0ee933186a2e7c37823cfd416e6acfba22b0..3c439c70a41322dae2ea2816b7a11ce1654fc976 100644
--- a/components/scheduler/child/scheduler_helper.h
+++ b/components/scheduler/child/scheduler_helper.h
@@ -15,7 +15,7 @@
 
 namespace scheduler {
 
-class SchedulerTaskRunnerDelegate;
+class NestableSingleThreadTaskRunner;
 
 // Common scheduler functionality for default tasks.
 class SCHEDULER_EXPORT SchedulerHelper {
@@ -23,11 +23,12 @@
   // NOTE |total_task_queue_count| must be >= TASK_QUEUE_COUNT.
   // Category strings must have application lifetime (statics or
   // literals). They may not include " chars.
-  SchedulerHelper(scoped_refptr<SchedulerTaskRunnerDelegate> 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);
+  SchedulerHelper(
+      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);
   ~SchedulerHelper();
 
   // Returns the default task runner.
@@ -104,7 +105,6 @@
   friend class SchedulerHelperTest;
 
   base::ThreadChecker thread_checker_;
-  scoped_refptr<SchedulerTaskRunnerDelegate> main_task_runner_;
   scoped_ptr<PrioritizingTaskQueueSelector> task_queue_selector_;
   scoped_ptr<TaskQueueManager> task_queue_manager_;