Integrate audible tab tracking into desktop engagement service.

chrome/browser/metrics/desktop_engagement_service.h

+// Copyright 2016 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 CHROME_BROWSER_METRICS_DESKTOP_ENGAGEMENT_SERVICE_H_
+#define CHROME_BROWSER_METRICS_DESKTOP_ENGAGEMENT_SERVICE_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+
+class DesktopEngagementService {
+ public:
+  static void Initialize();
+  static bool IsInitialized();
+  static DesktopEngagementService* Get();
+
+  void OnUserEvent();
+
+  void OnVisibilityChanged(bool visible);
+
+  void OnAudioStart();
+  void OnAudioEnd();
+
+ private:
+  DesktopEngagementService();
+  ~DesktopEngagementService();
+
+  void StartTimer(base::TimeDelta duration);
+  void OnTimerFired();
+
+  void StartSession();
+  void EndSession();
+
+  base::TimeTicks session_start_;
+  base::TimeTicks last_user_event_;
+
+  bool is_visible_ = false;
+  bool in_session_ = false;
+  bool is_audio_playing_ = false;
+
+  base::OneShotTimer timer_;
+
+  base::WeakPtrFactory<DesktopEngagementService> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DesktopEngagementService);
+};
+
+#endif  // CHROME_BROWSER_METRICS_DESKTOP_ENGAGEMENT_SERVICE_H_