cc: Add UniqueNotifier to cc/base.

cc/base/delayed_unique_notifier.h

+// 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.
+
+#ifndef CC_BASE_DELAYED_UNIQUE_NOTIFIER_H_
+#define CC_BASE_DELAYED_UNIQUE_NOTIFIER_H_
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace base {
+class SequencedTaskRunner;
+}  // namespace base
+
+namespace cc {
+
+class CC_EXPORT DelayedUniqueNotifier {
+ public:
+  // Configure this notifier to issue the |closure| notification in |delay| time
+  // from Schedule() call.
+  DelayedUniqueNotifier(base::SequencedTaskRunner* task_runner,
+                        const base::Closure& closure,
+                        const base::TimeDelta& delay);
+
+  // Destroying the notifier will ensure that no further notifications will
+  // happen from this class.
+  virtual ~DelayedUniqueNotifier();
+
+  // Schedule a notification to be run. If another notification is already
+  // pending, then it will happen in (at least) given delay from now. That is,
+  // if delay is 16ms and a notification has been scheduled 10ms ago (ie, it
+  // should trigger in no less than 6ms), then calling schedule will ensure that
+  // the only notification that arrives will happen in (at least) 16ms from now.
+  void Schedule();
+
+  // Cancel any previously scheduled runs.
+  void Cancel();
+
+ protected:
+  // Virtual for testing.
+  virtual base::TimeTicks Now() const;
+
+ private:
+  void NotifyIfTime();
+
+  base::SequencedTaskRunner* task_runner_;
+  base::Closure closure_;
+  base::TimeDelta delay_;
+  base::TimeTicks next_notification_time_;
+  bool notification_pending_;
+
+  base::WeakPtrFactory<DelayedUniqueNotifier> weak_ptr_factory_;
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_DELAYED_UNIQUE_NOTIFIER_H_