Rename DesktopEngagement* to DesktopSessionDuration*.

chrome/browser/metrics/desktop_engagement/chrome_visibility_observer.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/chrome_visibility_observer.h"
-
-#include "base/memory/singleton.h"
-#include "base/strings/string_number_conversions.h"
-#include "base/threading/thread_task_runner_handle.h"
-#include "chrome/browser/metrics/desktop_engagement/desktop_engagement_service.h"
-#include "chrome/browser/ui/browser.h"
-#include "chrome/browser/ui/browser_list.h"
-#include "components/variations/variations_associated_data.h"
-
-namespace metrics {
-
-ChromeVisibilityObserver::ChromeVisibilityObserver() : weak_factory_(this) {
-  BrowserList::AddObserver(this);
-  InitVisibilityGapTimeout();
-}
-
-ChromeVisibilityObserver::~ChromeVisibilityObserver() {
-  BrowserList::RemoveObserver(this);
-}
-
-void ChromeVisibilityObserver::SendVisibilityChangeEvent(bool active) {
-  DesktopEngagementService::Get()->OnVisibilityChanged(active);
-}
-
-void ChromeVisibilityObserver::CancelVisibilityChange() {
-  weak_factory_.InvalidateWeakPtrs();
-}
-
-void ChromeVisibilityObserver::OnBrowserSetLastActive(Browser* browser) {
-  if (weak_factory_.HasWeakPtrs())
-    CancelVisibilityChange();
-  else
-    SendVisibilityChangeEvent(true);
-}
-
-void ChromeVisibilityObserver::OnBrowserNoLongerActive(Browser* browser) {
-  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE,
-      base::Bind(&ChromeVisibilityObserver::SendVisibilityChangeEvent,
-                 weak_factory_.GetWeakPtr(), false),
-      visibility_gap_timeout_);
-}
-
-void ChromeVisibilityObserver::OnBrowserRemoved(Browser* browser) {
-  // If there are no browser instances left then we should notify that browser
-  // is not visible anymore immediately without waiting.
-  if (BrowserList::GetInstance()->empty()) {
-    CancelVisibilityChange();
-    SendVisibilityChangeEvent(false);
-  }
-}
-
-void ChromeVisibilityObserver::InitVisibilityGapTimeout() {
-  const int kDefaultVisibilityGapTimeout = 3;
-
-  int timeout_seconds = kDefaultVisibilityGapTimeout;
-  std::string param_value = variations::GetVariationParamValue(
-      "DesktopEngagement", "visibility_gap_timeout");
-  if (!param_value.empty())
-    base::StringToInt(param_value, &timeout_seconds);
-
-  visibility_gap_timeout_ = base::TimeDelta::FromSeconds(timeout_seconds);
-}
-
-}  // namespace metrics