Add desktop engagement metrics.

chrome/browser/metrics/desktop_engagement/desktop_engagement_service.cc

+// 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.
+
+#include "chrome/browser/metrics/desktop_engagement/desktop_engagement_service.h"
+
+#include "base/bind.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/strings/string_number_conversions.h"
+#include "components/variations/variations_associated_data.h"
+
+namespace metrics {
+
+namespace {
+
+DesktopEngagementService* g_instance = nullptr;
+
+}  // namespace
+
+// static
+void DesktopEngagementService::Initialize() {
+  g_instance = new DesktopEngagementService;
+}
+
+// static
+bool DesktopEngagementService::IsInitialized() {
+  return g_instance != nullptr;
+}
+
+// static
+DesktopEngagementService* DesktopEngagementService::Get() {
+  DCHECK(g_instance);
+  return g_instance;
+}
+
+void DesktopEngagementService::StartTimer(base::TimeDelta duration) {
+  timer_.Start(FROM_HERE, duration,
+               base::Bind(&DesktopEngagementService::OnTimerFired,
+                          weak_factory_.GetWeakPtr()));
+}
+
+void DesktopEngagementService::OnVisibilityChanged(bool visible) {
+  is_visible_ = visible;
+  if (is_visible_ && !is_first_session_) {
+    OnUserEvent();
+  } else if (in_session_ && !is_audio_playing_) {
+    DVLOG(4) << "Ending session due to visibility change";
+    EndSession();
+  }
+}
+
+void DesktopEngagementService::OnUserEvent() {
+  if (!is_visible_)
+    return;
+
+  last_user_event_ = base::TimeTicks::Now();
+  // This may start session.
+  if (!in_session_) {
+    DVLOG(4) << "Starting session due to user event";
+    StartSession();
+  }
+}
+
+void DesktopEngagementService::OnAudioStart() {
+  // This may start session.
+  is_audio_playing_ = true;
+  if (!in_session_) {
+    DVLOG(4) << "Starting session due to audio start";
+    StartSession();
+  }
+}
+
+void DesktopEngagementService::OnAudioEnd() {
+  is_audio_playing_ = false;
+
+  // If the timer is not running, this means that no user events happened in the
+  // last 5 minutes so the session can be terminated.
+  if (!timer_.IsRunning()) {
+    DVLOG(4) << "Ending session due to audio ending";
+    EndSession();
+  }
+}
+
+DesktopEngagementService::DesktopEngagementService()
+    : session_start_(base::TimeTicks::Now()),
+      last_user_event_(session_start_),
+      visibility_observer_(),

[Alexei Svitkine (slow), 2016/07/29 19:58:08]

Nit: You can omit this, the no argument constructor will just be run implicitly.

[gayane -on leave until 09-2017, 2016/08/01 16:39:18]

Done.

+      audio_tracker_(this),
+      weak_factory_(this) {
+  InitInactivityTimeout();
+}
+
+DesktopEngagementService::~DesktopEngagementService() {}
+
+void DesktopEngagementService::OnTimerFired() {
+  base::TimeDelta remaining =
+      inactivity_timeout_ - (base::TimeTicks::Now() - last_user_event_);
+  if (remaining.ToInternalValue() > 0) {
+    StartTimer(remaining);
+    return;
+  }
+
+  // No user events happened in the last 5 min. Terminate the session now.
+  if (!is_audio_playing_) {
+    DVLOG(4) << "Ending session after delay";
+    EndSession();
+  }
+}
+
+void DesktopEngagementService::StartSession() {
+  in_session_ = true;
+  is_first_session_ = false;
+  session_start_ = base::TimeTicks::Now();
+  StartTimer(inactivity_timeout_);
+}
+
+void DesktopEngagementService::EndSession() {
+  in_session_ = false;
+
+  base::TimeDelta delta = base::TimeTicks::Now() - session_start_;
+  DVLOG(4) << "Logging session length of " << delta.InSeconds() << " seconds.";
+
+  // Note: This metric is recorded separately for Android in
+  // UmaSessionStats::UmaEndSession.
+  UMA_HISTOGRAM_LONG_TIMES("Session.TotalDuration", delta);
+}
+
+void DesktopEngagementService::InitInactivityTimeout() {
+  const int kDefaultInactivityTimeoutMinutes = 5;
+
+  int timeout_minutes = kDefaultInactivityTimeoutMinutes;
+  std::string param_value = variations::GetVariationParamValue(
+      "DesktopEngagement", "inactivity_timeout");
+  if (!param_value.empty())
+    base::StringToInt(param_value, &timeout_minutes);
+
+  inactivity_timeout_ = base::TimeDelta::FromMinutes(timeout_minutes);
+}
+
+}  // namespace metrics