[DesktopSessionDurationTracker] Remove visibility-switch timeout from session length.

chrome/browser/metrics/desktop_session_duration/desktop_session_duration_tracker.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_session_duration/desktop_session_duration_tracker.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 {
 
 DesktopSessionDurationTracker* g_instance = nullptr;
 
+const base::TimeDelta kZeroTime = base::TimeDelta::FromSeconds(0);
+
 }  // namespace
 
 // static
 void DesktopSessionDurationTracker::Initialize() {
   g_instance = new DesktopSessionDurationTracker;
 }
 
 // static
 bool DesktopSessionDurationTracker::IsInitialized() {
   return g_instance != nullptr;
 }
 
 // static
 DesktopSessionDurationTracker* DesktopSessionDurationTracker::Get() {
   DCHECK(g_instance);
   return g_instance;
 }
 
 void DesktopSessionDurationTracker::StartTimer(base::TimeDelta duration) {
   timer_.Start(FROM_HERE, duration,
                base::Bind(&DesktopSessionDurationTracker::OnTimerFired,
                           weak_factory_.GetWeakPtr()));
 }
 
-void DesktopSessionDurationTracker::OnVisibilityChanged(bool visible) {
+void DesktopSessionDurationTracker::OnVisibilityChanged(
+    bool visible, base::TimeDelta time_ago) {
   is_visible_ = visible;
   if (is_visible_ && !is_first_session_) {
+    DCHECK(time_ago.is_zero());
     OnUserEvent();
   } else if (in_session_ && !is_audio_playing_) {
+    DCHECK(!visible);
     DVLOG(4) << "Ending session due to visibility change";
-    EndSession();
+    EndSession(time_ago);
   }
 }
 
 void DesktopSessionDurationTracker::OnUserEvent() {
   if (!is_visible_)
     return;
 
   last_user_event_ = base::TimeTicks::Now();
   // This may start session.
   if (!in_session_) {
@@ skipping 11 matching lines @@
   }
 }
 
 void DesktopSessionDurationTracker::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();
+    EndSession(kZeroTime);
   }
 }
 
 DesktopSessionDurationTracker::DesktopSessionDurationTracker()
     : session_start_(base::TimeTicks::Now()),
       last_user_event_(session_start_),
       audio_tracker_(this),
       weak_factory_(this) {
   InitInactivityTimeout();
 }
 
 DesktopSessionDurationTracker::~DesktopSessionDurationTracker() {}
 
 void DesktopSessionDurationTracker::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();
+    EndSession(inactivity_timeout_);
   }
 }
 
 void DesktopSessionDurationTracker::StartSession() {
   in_session_ = true;
   is_first_session_ = false;
   session_start_ = base::TimeTicks::Now();
   StartTimer(inactivity_timeout_);
 }
 
-void DesktopSessionDurationTracker::EndSession() {
+void DesktopSessionDurationTracker::EndSession(
+    base::TimeDelta time_to_discount) {
   in_session_ = false;
 
   base::TimeDelta delta = base::TimeTicks::Now() - session_start_;
 
-  // If timer is not running then session ended because of inactivity.
-  if (!timer_.IsRunning())
-    delta -= inactivity_timeout_;
+  // Trim any timeouts from the session length and lower bound to a session of
+  // length 0.
+  delta -= time_to_discount;
+  if (delta < kZeroTime)
+    delta = kZeroTime;
 
   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 DesktopSessionDurationTracker::InitInactivityTimeout() {
   const int kDefaultInactivityTimeoutMinutes = 5;
 
   int timeout_minutes = kDefaultInactivityTimeoutMinutes;
   std::string param_value = variations::GetVariationParamValue(
       "DesktopSessionDuration", "inactivity_timeout");
   if (!param_value.empty())
     base::StringToInt(param_value, &timeout_minutes);
 
   inactivity_timeout_ = base::TimeDelta::FromMinutes(timeout_minutes);
 }
 
 }  // namespace metrics