Introduce ChildScheduler as common base interface for WorkerScheduler and RendererScheduler.

content/child/scheduler/worker_scheduler_impl.h

Index: content/child/scheduler/worker_scheduler_impl.h
diff --git a/content/child/scheduler/worker_scheduler_impl.h b/content/child/scheduler/worker_scheduler_impl.h
index 186d2bcb53ac0b3483c51560f676be9b040c4957..043476dbf627f7356299964e0ac12d26cb025fb6 100644
--- a/content/child/scheduler/worker_scheduler_impl.h
+++ b/content/child/scheduler/worker_scheduler_impl.h
@@ -30,6 +30,7 @@ class CONTENT_EXPORT WorkerSchedulerImpl
   scoped_refptr<base::SingleThreadTaskRunner> DefaultTaskRunner() override;
   scoped_refptr<SingleThreadIdleTaskRunner> IdleTaskRunner() override;
   bool CanExceedIdleDeadlineIfRequired() const override;
+  bool ShouldYieldForHighPriorityWork() override;
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer) override;
   void RemoveTaskObserver(
       base::MessageLoop::TaskObserver* task_observer) override;