compositor worker: Use a WebThread for the compositor thread.

components/scheduler/child/worker_scheduler_impl.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 "components/scheduler/child/worker_scheduler_impl.h"
 
 #include "base/bind.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "components/scheduler/base/task_queue.h"
@@ skipping 21 matching lines @@
 WorkerSchedulerImpl::~WorkerSchedulerImpl() {
   TRACE_EVENT_OBJECT_DELETED_WITH_ID(
       TRACE_DISABLED_BY_DEFAULT("worker.scheduler"), "WorkerScheduler", this);
 }
 
 void WorkerSchedulerImpl::Init() {
   initialized_ = true;
   idle_helper_.EnableLongIdlePeriod();
 }
 
-scoped_refptr<TaskQueue> WorkerSchedulerImpl::DefaultTaskRunner() {
+scoped_refptr<base::SingleThreadTaskRunner>
+WorkerSchedulerImpl::DefaultTaskRunner() {
   DCHECK(initialized_);
   return helper_.DefaultTaskRunner();
 }
 
 scoped_refptr<SingleThreadIdleTaskRunner>
 WorkerSchedulerImpl::IdleTaskRunner() {
   DCHECK(initialized_);
   return idle_helper_.IdleTaskRunner();
 }
 
@@ skipping 31 matching lines @@
 bool WorkerSchedulerImpl::CanEnterLongIdlePeriod(base::TimeTicks,
                                                  base::TimeDelta*) {
   return true;
 }
 
 base::TimeTicks WorkerSchedulerImpl::CurrentIdleTaskDeadlineForTesting() const {
   return idle_helper_.CurrentIdleTaskDeadline();
 }
 
 }  // namespace scheduler