Add a simple scheduler for animation frames

mc/scheduler/scheduler.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 "mc/scheduler/scheduler.h"
+
+namespace mc {
+
+Scheduler::Client::~Client() {
+}
+
+Scheduler::Scheduler(Client* client,
+                     scoped_refptr<base::SingleThreadTaskRunner> task_runner)
+    : client_(client), timer_(this, task_runner) {
+}
+
+Scheduler::~Scheduler() {
+}
+
+void Scheduler::SetNeedsFrame() {
+  timer_.SetEnabled(true);
+}
+
+void Scheduler::UpdateFrameDuration(base::TimeDelta estimate) {
+  frame_duration_ = estimate;
+  UpdateTimerInterval();
+}
+
+void Scheduler::UpdateVSync(const TimeInterval& vsync) {
+  vsync_ = vsync;
+  UpdateTimerInterval();
+}
+
+void Scheduler::UpdateTimerInterval() {
+  TimeInterval interval = vsync_;
+  interval.base -= frame_duration_;
+  timer_.SetInterval(interval);
+}
+
+void Scheduler::OnTimerTick(base::TimeTicks now) {
+  timer_.SetEnabled(false);
+  client_->BeginFrame(now, vsync_.NextAfter(now));
+  // We might be deleted here.
+}
+}