[scheduler]: Avoid waking up the scheduler to end long idle periods.

components/scheduler/child/null_idle_task_runner.cc

 // Copyright 2014 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/null_idle_task_runner.h"
 
 namespace scheduler {
 
 NullIdleTaskRunner::NullIdleTaskRunner()
     : SingleThreadIdleTaskRunner(nullptr,
                                  nullptr,
-                                 base::Callback<void(base::TimeTicks*)>(),
+                                 nullptr,
                                  "null.taskrunner") {
 }
 
 NullIdleTaskRunner::~NullIdleTaskRunner() {
 }
 
 void NullIdleTaskRunner::PostIdleTask(
     const tracked_objects::Location& from_here,
     const IdleTask& idle_task) {
 }
 
 void NullIdleTaskRunner::PostNonNestableIdleTask(
     const tracked_objects::Location& from_here,
     const IdleTask& idle_task) {
 }
 
 void NullIdleTaskRunner::PostIdleTaskAfterWakeup(
     const tracked_objects::Location& from_here,
     const IdleTask& idle_task) {
 }
 
 }  // namespace scheduler