compositor worker: Use a WebThread for the compositor thread.

components/scheduler/child/webthread_impl_for_worker_scheduler.cc

Index: components/scheduler/child/webthread_impl_for_worker_scheduler.cc
diff --git a/components/scheduler/child/webthread_impl_for_worker_scheduler.cc b/components/scheduler/child/webthread_impl_for_worker_scheduler.cc
index afdcb6d50322a49b1a1a1f83c594086ac5b3f467..345ecef9690b20b189084f190bcf708e2f0ead33 100644
--- a/components/scheduler/child/webthread_impl_for_worker_scheduler.cc
+++ b/components/scheduler/child/webthread_impl_for_worker_scheduler.cc
@@ -29,7 +29,9 @@ WebThreadImplForWorkerScheduler::WebThreadImplForWorkerScheduler(
   bool started = thread_->StartWithOptions(options);
   CHECK(started);
   thread_task_runner_ = thread_->task_runner();
+}
 
+void WebThreadImplForWorkerScheduler::Init() {
   base::WaitableEvent completion(false, false);
   thread_task_runner_->PostTask(
       FROM_HERE, base::Bind(&WebThreadImplForWorkerScheduler::InitOnThread,
@@ -38,13 +40,15 @@ WebThreadImplForWorkerScheduler::WebThreadImplForWorkerScheduler(
 }
 
 WebThreadImplForWorkerScheduler::~WebThreadImplForWorkerScheduler() {
-  base::WaitableEvent completion(false, false);
-  // Restore the original task runner so that the thread can tear itself down.
-  thread_task_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&WebThreadImplForWorkerScheduler::RestoreTaskRunnerOnThread,
-                 base::Unretained(this), &completion));
-  completion.Wait();
+  if (task_runner_delegate_) {
+    base::WaitableEvent completion(false, false);
+    // Restore the original task runner so that the thread can tear itself down.
+    thread_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&WebThreadImplForWorkerScheduler::RestoreTaskRunnerOnThread,
+                   base::Unretained(this), &completion));
+    completion.Wait();
+  }
   thread_->Stop();
 }
 
@@ -52,9 +56,7 @@ void WebThreadImplForWorkerScheduler::InitOnThread(
     base::WaitableEvent* completion) {
   // TODO(alexclarke): Do we need to unify virtual time for workers and the
   // main thread?
-  task_runner_delegate_ = SchedulerTqmDelegateImpl::Create(
-      thread_->message_loop(), make_scoped_ptr(new base::DefaultTickClock()));
-  worker_scheduler_ = WorkerScheduler::Create(task_runner_delegate_);
+  worker_scheduler_ = CreateWorkerScheduler();
   worker_scheduler_->Init();
   task_runner_ = worker_scheduler_->DefaultTaskRunner();
   idle_task_runner_ = worker_scheduler_->IdleTaskRunner();
@@ -80,6 +82,13 @@ void WebThreadImplForWorkerScheduler::WillDestroyCurrentMessageLoop() {
   worker_scheduler_.reset();
 }
 
+scoped_ptr<scheduler::WorkerScheduler>
+WebThreadImplForWorkerScheduler::CreateWorkerScheduler() {
+  task_runner_delegate_ = SchedulerTqmDelegateImpl::Create(
+      thread_->message_loop(), make_scoped_ptr(new base::DefaultTickClock()));
+  return WorkerScheduler::Create(task_runner_delegate_);
+}
+
 blink::PlatformThreadId WebThreadImplForWorkerScheduler::threadId() const {
   return thread_->GetThreadId();
 }