cc: Add UniqueNotifier to cc/base.

cc/base/delayed_unique_notifier.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 "cc/base/delayed_unique_notifier.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/location.h"
+#include "base/sequenced_task_runner.h"
+
+namespace cc {
+
+DelayedUniqueNotifier::DelayedUniqueNotifier(
+    base::SequencedTaskRunner* task_runner,
+    const base::Closure& closure,
+    const base::TimeDelta& delay)
+    : task_runner_(task_runner),
+      closure_(closure),
+      delay_(delay),
+      notification_pending_(false),
+      weak_ptr_factory_(this) {
+}
+
+DelayedUniqueNotifier::~DelayedUniqueNotifier() {
+}
+
+void DelayedUniqueNotifier::Schedule() {
+  if (notification_pending_) {
+    next_notification_time_ = base::TimeTicks::Now() + delay_;
+    return;
+  }
+
+  next_notification_time_ = base::TimeTicks::Now() + delay_;
+  task_runner_->PostDelayedTask(FROM_HERE,
+                                base::Bind(&DelayedUniqueNotifier::NotifyIfTime,
+                                           weak_ptr_factory_.GetWeakPtr()),
+                                delay_);
+  notification_pending_ = true;
+}
+
+void DelayedUniqueNotifier::Cancel() {
+  weak_ptr_factory_.InvalidateWeakPtrs();

[reveman, 2014/05/22 23:24:28]

This is going to be a problem as calling Schedule() and Cancel() repeatably will
cause the message pump task queue to fill up. Maybe you can set
next_notification_time_ to base::TimeTicks() instead.

[vmpstr, 2014/05/27 18:14:59]

Makes sense. Done. Now it should only ever have one task in the task queue.

+  notification_pending_ = false;
+}
+
+void DelayedUniqueNotifier::NotifyIfTime() {
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (next_notification_time_ > now) {
+    task_runner_->PostDelayedTask(
+        FROM_HERE,
+        base::Bind(&DelayedUniqueNotifier::NotifyIfTime,
+                   weak_ptr_factory_.GetWeakPtr()),
+        next_notification_time_ - now);
+    return;
+  }
+
+  // Note the order here is important since closure might schedule another run.
+  notification_pending_ = false;
+  closure_.Run();
+}
+
+}  // namespace cc