ash:Shelf - Added UMA stats for ShelfAlignment

ash/periodic_metrics_recorder.h

Index: ash/periodic_metrics_recorder.h
diff --git a/ash/periodic_metrics_recorder.h b/ash/periodic_metrics_recorder.h
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+// Copyright (c) 2013 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 ASH_PERIODIC_METRICS_RECORDER_H_
+#define ASH_PERIODIC_METRICS_RECORDER_H_
+
+#include "base/timer/timer.h"
+
+namespace ash {
+
+// Periodic Metrics Recorder provides a repeating callback (RecordMetrics)
+// on a timer to allow recording of state data over time to the UMA records.
+// Any additional states (in ash) that require monitoring can be added to
+// this class.
+class PeriodicMetricsRecorder {
+ public:
+  PeriodicMetricsRecorder();
+  ~PeriodicMetricsRecorder();
+
+ private:
+  void RecordMetrics();
+
+  base::RepeatingTimer<PeriodicMetricsRecorder> timer_;
+};
+
+}  // namespace ash
+
+#endif  // ASH_PERIODIC_METRICS_RECORDER_H_