scheduler: Fix debug build crash with --disable-blink-scheduler

content/renderer/scheduler/single_thread_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 "content/renderer/scheduler/single_thread_idle_task_runner.h"
 
 #include "base/location.h"
 #include "base/trace_event/trace_event.h"
 
 namespace content {
 
 SingleThreadIdleTaskRunner::SingleThreadIdleTaskRunner(
     scoped_refptr<base::SingleThreadTaskRunner> idle_priority_task_runner,
     scoped_refptr<base::SingleThreadTaskRunner> after_wakeup_task_runner,
     base::Callback<void(base::TimeTicks*)> deadline_supplier)
     : idle_priority_task_runner_(idle_priority_task_runner),
       after_wakeup_task_runner_(after_wakeup_task_runner),
       deadline_supplier_(deadline_supplier) {
-  DCHECK(idle_priority_task_runner_->RunsTasksOnCurrentThread());
-  DCHECK(after_wakeup_task_runner_->RunsTasksOnCurrentThread());
+  DCHECK(!idle_priority_task_runner_ ||
+         idle_priority_task_runner_->RunsTasksOnCurrentThread());
+  DCHECK(!after_wakeup_task_runner_ ||
+         after_wakeup_task_runner_->RunsTasksOnCurrentThread());
 }
 
 SingleThreadIdleTaskRunner::~SingleThreadIdleTaskRunner() {
 }
 
 bool SingleThreadIdleTaskRunner::RunsTasksOnCurrentThread() const {
   return idle_priority_task_runner_->RunsTasksOnCurrentThread();
 }
 
 void SingleThreadIdleTaskRunner::PostIdleTask(
@@ skipping 22 matching lines @@
   bool is_tracing;
   TRACE_EVENT_CATEGORY_GROUP_ENABLED("renderer.scheduler", &is_tracing);
   if (is_tracing && base::TimeTicks::Now() > deadline) {
     TRACE_EVENT_INSTANT0("renderer.scheduler",
                          "SingleThreadIdleTaskRunner::DidOverrunDeadline",
                          TRACE_EVENT_SCOPE_THREAD);
   }
 }
 
 }  // namespace content