Add a WorkerScheduler and a WebThreadImplForWorker

content/renderer/scheduler/webthread_impl_for_scheduler.h

Index: content/renderer/scheduler/webthread_impl_for_scheduler.h
diff --git a/content/renderer/scheduler/webthread_impl_for_scheduler.h b/content/renderer/scheduler/webthread_impl_for_scheduler.h
index 36bd2e2a2e7f004a57c273c180520b7b36e65522..c75957e3566313826bb5e451cc60ef2a50734ac6 100644
--- a/content/renderer/scheduler/webthread_impl_for_scheduler.h
+++ b/content/renderer/scheduler/webthread_impl_for_scheduler.h
@@ -23,6 +23,7 @@ class CONTENT_EXPORT WebThreadImplForScheduler : public WebThreadBase {
 
   // WebThreadBase implementation.
   base::SingleThreadTaskRunner* TaskRunner() const override;
+  SingleThreadIdleTaskRunner* IdleTaskRunner() const override;
 
  private:
   base::MessageLoop* MessageLoop() const override;
@@ -32,6 +33,7 @@ class CONTENT_EXPORT WebThreadImplForScheduler : public WebThreadBase {
       base::MessageLoop::TaskObserver* observer) override;
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+  scoped_refptr<SingleThreadIdleTaskRunner> idle_task_runner_;
   RendererScheduler* scheduler_;  // Not owned.
   blink::PlatformThreadId thread_id_;
 };