compositor worker: Use a WebThread for the compositor thread.

components/scheduler/child/compositor_worker_scheduler.cc

+// 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.
+
+#include "components/scheduler/child/compositor_worker_scheduler.h"
+
+#include "base/message_loop/message_loop.h"
+#include "base/threading/thread.h"
+
+namespace scheduler {
+
+CompositorWorkerScheduler::CompositorWorkerScheduler(base::Thread* thread)
+    : thread_(thread) {}
+
+CompositorWorkerScheduler::~CompositorWorkerScheduler() {}
+
+void CompositorWorkerScheduler::Init() {}
+
+scoped_refptr<base::SingleThreadTaskRunner>
+CompositorWorkerScheduler::DefaultTaskRunner() {
+  // TODO(sad): Implement a more robust scheduler that can do idle tasks for GC
+  // without regressing performance of the rest of the system.
+  return thread_->task_runner();
+}
+
+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;
+}
+
+bool CompositorWorkerScheduler::CanExceedIdleDeadlineIfRequired() const {
+  return false;
+}
+
+bool CompositorWorkerScheduler::ShouldYieldForHighPriorityWork() {
+  return false;
+}
+
+void CompositorWorkerScheduler::AddTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+  thread_->message_loop()->AddTaskObserver(task_observer);
+}
+
+void CompositorWorkerScheduler::RemoveTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+  thread_->message_loop()->RemoveTaskObserver(task_observer);
+}
+
+void CompositorWorkerScheduler::Shutdown() {}
+
+}  // namespace scheduler