diff --git a/buffet/states/state_change_queue_interface.h b/buffet/states/state_change_queue_interface.h
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+++ b/buffet/states/state_change_queue_interface.h
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+// Copyright 2014 The Chromium OS 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 BUFFET_STATES_STATE_CHANGE_QUEUE_INTERFACE_H_
+#define BUFFET_STATES_STATE_CHANGE_QUEUE_INTERFACE_H_
+
+#include <vector>
+
+#include <base/time/time.h>
+#include <chromeos/variant_dictionary.h>
+
+namespace buffet {
+
+// A simple notification record event to track device state changes.
+// The |timestamp| records the time of the state change.
+// |property_set| contains a property set with the new property values.
+// The property set contains only the properties updated at the time the event
+// was recorded.
+struct StateChange {
+  base::Time timestamp;
+  chromeos::VariantDictionary property_set;
+};
+
+// An abstract interface to StateChangeQueue to record and retrieve state
+// change notification events.
+class StateChangeQueueInterface {
+ public:
+  // Returns true if the state change notification queue is empty.
+  virtual bool IsEmpty() const = 0;
+
+  // Called by StateManager when device state properties are updated.
+  virtual bool NotifyPropertiesUpdated(const StateChange& change) = 0;
+
+  // Returns the recorded state changes since last time this method was called.
+  virtual std::vector<StateChange> GetAndClearRecordedStateChanges() = 0;
+
+ protected:
+  // No one should attempt do destroy the queue through the interface.
+  ~StateChangeQueueInterface() {}
+};
+
+}  // namespace buffet
+
+#endif  // BUFFET_STATES_STATE_CHANGE_QUEUE_INTERFACE_H_