compositor worker: Use a WebThread for the compositor thread.

components/scheduler/child/webthread_impl_for_worker_scheduler.cc

 // Copyright 2015 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/webthread_impl_for_worker_scheduler.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
@@ skipping 11 matching lines @@
     const char* name)
     : WebThreadImplForWorkerScheduler(name, base::Thread::Options()) {}
 
 WebThreadImplForWorkerScheduler::WebThreadImplForWorkerScheduler(
     const char* name,
     base::Thread::Options options)
     : thread_(new base::Thread(name ? name : std::string())) {
   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,
                             base::Unretained(this), &completion));
   completion.Wait();
 }
 
 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();
   thread_->Stop();
 }
 
 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_->Init();
-  task_runner_ = worker_scheduler_->DefaultTaskRunner();
+  if (UseThreadTaskRunnerAsDefault())
+    task_runner_ = thread_task_runner_;
+  else
+    task_runner_ = worker_scheduler_->DefaultTaskRunner();
   idle_task_runner_ = worker_scheduler_->IdleTaskRunner();
   web_scheduler_.reset(new WebSchedulerImpl(
       worker_scheduler_.get(), worker_scheduler_->IdleTaskRunner(),
       worker_scheduler_->DefaultTaskRunner(),
       worker_scheduler_->DefaultTaskRunner()));
   base::MessageLoop::current()->AddDestructionObserver(this);
   web_task_runner_ = make_scoped_ptr(new WebTaskRunnerImpl(task_runner_));
   completion->Signal();
 }
 
 void WebThreadImplForWorkerScheduler::RestoreTaskRunnerOnThread(
     base::WaitableEvent* completion) {
   task_runner_delegate_->RestoreDefaultTaskRunner();
   completion->Signal();
 }
 
 void WebThreadImplForWorkerScheduler::WillDestroyCurrentMessageLoop() {
   task_runner_ = nullptr;
   idle_task_runner_ = nullptr;
   web_scheduler_.reset();
   worker_scheduler_.reset();
 }
 
+bool WebThreadImplForWorkerScheduler::UseThreadTaskRunnerAsDefault() const {
+  return false;
+}
+
 blink::PlatformThreadId WebThreadImplForWorkerScheduler::threadId() const {
   return thread_->GetThreadId();
 }
 
 blink::WebScheduler* WebThreadImplForWorkerScheduler::scheduler() const {
   return web_scheduler_.get();
 }
 
 base::SingleThreadTaskRunner* WebThreadImplForWorkerScheduler::TaskRunner()
     const {
@@ skipping 13 matching lines @@
     base::MessageLoop::TaskObserver* observer) {
   worker_scheduler_->AddTaskObserver(observer);
 }
 
 void WebThreadImplForWorkerScheduler::RemoveTaskObserverInternal(
     base::MessageLoop::TaskObserver* observer) {
   worker_scheduler_->RemoveTaskObserver(observer);
 }
 
 }  // namespace scheduler