Observe input metrics from web content area.

chrome/browser/metrics/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_service.h"
+
+#include "base/bind.h"
+#include "base/metrics/histogram_macros.h"
+#include "chrome/browser/metrics/chrome_visibility_observer.h"
+
+
+namespace {
+
+DesktopEngagementService* g_instance = nullptr;
+
+const int kActivityIntervalMinutes = 1;
+
+}  // namespace
+
+// static
+void DesktopEngagementService::Initialize() {
+  g_instance = new DesktopEngagementService;
+  metrics::ChromeVisibilityObserver::Initialize();
+}
+
+// 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_) {
+    OnUserEvent();
+  } else if (in_session_) {
+    DLOG(ERROR) << "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_) {
+    DLOG(ERROR) << "Starting session due to user event";
+    StartSession();
+  }
+}
+
+void DesktopEngagementService::OnAudioStart() {
+  // This may start session.
+  is_audio_playing_ = true;
+  if (!in_session_) {
+    DLOG(ERROR) << "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()) {
+    DLOG(ERROR) << "Ending session due to audio ending";
+    EndSession();
+  }
+}
+
+DesktopEngagementService::DesktopEngagementService()
+    : session_start_(base::TimeTicks::Now()), last_user_event_(session_start_),
+      weak_factory_(this) {
+  StartSession();
+  // TODO: Add user events observers here, or add a static Get() method to
+  //       DesktopEngagementService.
+}
+
+DesktopEngagementService::~DesktopEngagementService() {
+}
+
+void DesktopEngagementService::OnTimerFired() {
+  base::TimeDelta remaining = base::TimeTicks::Now() - last_user_event_;
+  if (remaining < base::TimeDelta::FromMinutes(kActivityIntervalMinutes)) {
+    StartTimer(remaining);
+    return;
+  }
+
+  // No user events happened in the last 5 min. Terminate the session now.
+  if (!is_audio_playing_) {
+    DLOG(ERROR) << "Ending session after delay";
+    EndSession();
+  }
+}
+
+void DesktopEngagementService::StartSession() {
+  in_session_ = true;
+  session_start_ = base::TimeTicks::Now();
+  StartTimer(base::TimeDelta::FromMinutes(kActivityIntervalMinutes));
+}
+
+void DesktopEngagementService::EndSession() {
+  in_session_ = false;
+  base::TimeDelta delta = base::TimeTicks::Now() - session_start_;
+
+  constexpr unsigned kNumTimeSlices = 60 / 5 * 24;
+  DLOG(ERROR) << "Logging session length of " << delta.InSeconds()
+              << " seconds.";
+  UMA_HISTOGRAM_CUSTOM_TIMES("Session.TotalDuration", delta,
+                             base::TimeDelta::FromMilliseconds(1),
+                             base::TimeDelta::FromHours(24), kNumTimeSlices);
+}