compositor worker: Use a WebThread for the compositor thread.

components/scheduler/child/compositor_worker_scheduler.h

+// Copyright 2016 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.
+
+#ifndef COMPONENTS_SCHEDULER_CHILD_COMPOSITOR_WORKER_SCHEDULER_H_
+#define COMPONENTS_SCHEDULER_CHILD_COMPOSITOR_WORKER_SCHEDULER_H_
+
+#include "base/macros.h"
+#include "components/scheduler/child/worker_scheduler.h"
+#include "components/scheduler/scheduler_export.h"
+
+namespace base {
+class Thread;
+}
+
+namespace scheduler {
+
+class SCHEDULER_EXPORT CompositorWorkerScheduler : public WorkerScheduler {
+ public:
+  explicit CompositorWorkerScheduler(base::Thread* thread);
+  ~CompositorWorkerScheduler() override;
+
+  // WorkerScheduler:
+  void Init() override;
+
+  // ChildScheduler:
+  scoped_refptr<base::SingleThreadTaskRunner> DefaultTaskRunner() override;
+  scoped_refptr<scheduler::SingleThreadIdleTaskRunner> IdleTaskRunner()
+      override;
+  bool ShouldYieldForHighPriorityWork() override;
+  bool CanExceedIdleDeadlineIfRequired() const override;
+  void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer) override;
+  void RemoveTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) override;
+  void Shutdown() override;
+
+ private:
+  base::Thread* thread_;
+
+  DISALLOW_COPY_AND_ASSIGN(CompositorWorkerScheduler);
+};
+
+}  // namespace scheduler
+
+#endif  // COMPONENTS_SCHEDULER_CHILD_COMPOSITOR_WORKER_SCHEDULER_H_