Record swap metrics

content/browser/memory/swap_metrics_observer.h

+// Copyright 2017 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 CONTENT_BROWSER_MEMORY_SWAP_METRICS_OBSERVER_H_
+#define CONTENT_BROWSER_MEMORY_SWAP_METRICS_OBSERVER_H_
+
+#include "base/memory/singleton.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+
+namespace content {
+
+// This class observes system's swapping behavior to collect metrics.
+// Metrics can be platform-specific.
+class SwapMetricsObserver {
+ public:
+  // This returns nullptr when swap metrics are not available on the system.
+  static SwapMetricsObserver* GetInstance();
+
+  // Starts observing swap metrics.
+  void Start();
+
+  // Stop observing swap metrics.
+  void Stop();
+
+ protected:
+  SwapMetricsObserver();
+  virtual ~SwapMetricsObserver();
+
+  // Periodically called to update swap metrics.
+  void UpdateMetrics();
+
+  // Platform-dependent parts of UpdateMetrics(). |interval| is the elapsed time
+  // since the last UpdateMetrics() call. |interval| will be zero when this
+  // function is called for the first time.
+  virtual void UpdateMetricsInternal(base::TimeDelta interval) = 0;
+
+ private:
+  // The interval between metrics updates.
+  base::TimeDelta update_interval_;
+
+  // A periodic timer to update swap metrics.
+  base::RepeatingTimer timer_;
+
+  // Holds the last TimeTicks when swap metrics are updated.
+  base::TimeTicks last_ticks_;
+
+  DISALLOW_COPY_AND_ASSIGN(SwapMetricsObserver);
+};
+
+}  // namespace
+
+#endif  // CONTENT_BROWSER_MEMORY_SWAP_METRICS_OBSERVER_H_