cc: Add UniqueNotifier to cc/base.

cc/base/unique_notifier.h

Index: cc/base/unique_notifier.h
diff --git a/cc/base/unique_notifier.h b/cc/base/unique_notifier.h
new file mode 100644
index 0000000000000000000000000000000000000000..4752f6f6955684d10adaf8de1317a943f9244a4d
--- /dev/null
+++ b/cc/base/unique_notifier.h
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+// 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_UNIQUE_NOTIFIER_H_
+#define CC_BASE_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 UniqueNotifier {
+ public:
+  // Configure this notifier to issue the |closure| notification when scheduled.
+  UniqueNotifier(base::SequencedTaskRunner* task_runner,
+                 const base::Closure& closure);
+
+  // Destroying the notifier will ensure that no further notifications will
+  // happen from this class.
+  ~UniqueNotifier();
+
+  // Schedule a notification to be run. If another notification is already
+  // pending, then only one notification will take place.
+  void Schedule();
+
+ private:
+  void Notify();
+
+  base::SequencedTaskRunner* task_runner_;
+  base::Closure closure_;
+  bool notification_pending_;
+
+  base::WeakPtrFactory<UniqueNotifier> weak_ptr_factory_;
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_UNIQUE_NOTIFIER_H_