Add desktop engagement metrics.

chrome/browser/metrics/desktop_engagement/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_DESKTOP_ENGAGEMENT_SERVICE_H_
+#define CHROME_BROWSER_METRICS_DESKTOP_ENGAGEMENT_DESKTOP_ENGAGEMENT_SERVICE_H_
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+
+namespace metrics {
+
+// Class for tracking and recording user engagement based on browser visibility,
+// audio and user interaction.
+class DesktopEngagementService {
+ public:
+  // Creates the |DesktopEngagementService| instance and initializes the
+  // observes that notify to it.
+  static void Initialize();
+
+  // Returns true if the |DesktopEngagementService| instance has been created.
+  static bool IsInitialized();
+
+  // Returns the |DesktopEngagementService| instance.
+  static DesktopEngagementService* Get();
+
+  // Called when user interaction with the browser is caught.
+  void OnUserEvent();
+
+  // Called when visibility of the browser changes.
+  void OnVisibilityChanged(bool visible);
+
+  // Called when audio starts or ends.
+  void OnAudioStart();
+  void OnAudioEnd();
+
+ protected:
+  DesktopEngagementService();
+  ~DesktopEngagementService();
+
+  // Decides whether session should be ended. Called when timer for inactivity
+  // timeout was fired. Overridden by tests.
+  virtual void OnTimerFired();
+
+  // Used for marking current state of the user engagement.

[Alexei Svitkine (slow), 2016/07/28 18:37:22]

Data members should not be protected, per the style guide. ("Note that data
members should be private.").

If these need to be accessed by tests, add protected accessors functions or
ForTesting() functions.

[gayane -on leave until 09-2017, 2016/07/28 21:21:34]

moved the functions to public.

+  bool is_visible_ = false;
+  bool in_session_ = false;
+  bool is_audio_playing_ = false;
+  bool is_first_session_ = true;
+
+  // Timeout for waiting for user interaction.
+  base::TimeDelta inactivity_timeout_;
+
+ private:
+  // Starts timer based on |inactivity_timeout_|.
+  void StartTimer(base::TimeDelta duration);
+
+  // Marks the start of the session.
+  void StartSession();
+
+  // Ends the session and saves session information into histograms.
+  void EndSession();
+
+  // Sets |inactivity_timeout_| based on variation params.
+  void InitInactivityTimeout();
+
+  // Used for marking start if the session.
+  base::TimeTicks session_start_;
+
+  // Used for marking last user interaction.
+  base::TimeTicks last_user_event_;
+
+  base::OneShotTimer timer_;
+
+  base::WeakPtrFactory<DesktopEngagementService> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DesktopEngagementService);
+};
+
+}  // namespace metrics
+
+#endif  // CHROME_BROWSER_METRICS_DESKTOP_ENGAGEMENT_DESKTOP_ENGAGEMENT_SERVICE_H_