compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

components/scheduler/child/compositor_worker_scheduler.cc

Index: components/scheduler/child/compositor_worker_scheduler.cc
diff --git a/components/scheduler/child/compositor_worker_scheduler.cc b/components/scheduler/child/compositor_worker_scheduler.cc
index 38a8a4a5129a03c043863e94f4ed5d657c4f0bae..c6e753d1e239b22abbb059d35ea19b781430c076 100644
--- a/components/scheduler/child/compositor_worker_scheduler.cc
+++ b/components/scheduler/child/compositor_worker_scheduler.cc
@@ -123,9 +123,9 @@ scoped_refptr<TaskQueue> CompositorWorkerScheduler::DefaultTaskRunner() {
 
 scoped_refptr<scheduler::SingleThreadIdleTaskRunner>
 CompositorWorkerScheduler::IdleTaskRunner() {
-  // TODO(sad): Not having a task-runner for idle tasks means v8 has to fallback
-  // to inline GC, which might cause jank.
-  return nullptr;
+  return make_scoped_refptr(new SingleThreadIdleTaskRunner(
+      thread_->task_runner(), thread_->task_runner(), this,
+      "compositor.scheduler"));
 }
 
 bool CompositorWorkerScheduler::CanExceedIdleDeadlineIfRequired() const {
@@ -148,4 +148,13 @@ void CompositorWorkerScheduler::RemoveTaskObserver(
 
 void CompositorWorkerScheduler::Shutdown() {}
 
+void CompositorWorkerScheduler::OnIdleTaskPosted() {}
+
+base::TimeTicks CompositorWorkerScheduler::WillProcessIdleTask() {
+  // TODO(flackr): Return the next frame time as the deadline instead.
+  return base::TimeTicks::Now() + base::TimeDelta::FromMillisecondsD(16.7);
+}
+
+void CompositorWorkerScheduler::DidProcessIdleTask() {}
+
 }  // namespace scheduler