Add metrics to keep track of the tab activate/deactivate cycle

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc

 // Copyright (c) 2013 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/chrome_browser_main_extra_parts_metrics.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/cpu.h"
 #include "base/macros.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/sys_info.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/about_flags.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_browser_main.h"
 #include "chrome/browser/mac/bluetooth_utility.h"
 #include "chrome/browser/shell_integration.h"
+#include "chrome/browser/metrics/tab_usage_recorder.h"

[Georges Khalil, 2016/09/14 16:10:16]

nit: order.

[Patrick Monette, 2016/09/16 00:13:59]

Done.

 #include "components/flags_ui/pref_service_flags_storage.h"
 #include "content/public/browser/browser_thread.h"
 #include "ui/base/touch/touch_device.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/display/screen.h"
 #include "ui/events/event_switches.h"
 
 #if !defined(OS_ANDROID)
 #include "chrome/browser/metrics/first_web_contents_profiler.h"
 #endif  // !defined(OS_ANDROID)
@@ skipping 329 matching lines @@
 #endif  // defined(OS_WIN)
 
   display_count_ = display::Screen::GetScreen()->GetNumDisplays();
   UMA_HISTOGRAM_COUNTS_100("Hardware.Display.Count.OnStartup", display_count_);
   display::Screen::GetScreen()->AddObserver(this);
   is_screen_observer_ = true;
 
 #if !defined(OS_ANDROID)
   FirstWebContentsProfiler::Start();
 #endif  // !defined(OS_ANDROID)
+
+  metrics::TabUsageRecorder::Initialize();
 }
 
 void ChromeBrowserMainExtraPartsMetrics::OnDisplayAdded(
     const display::Display& new_display) {
   EmitDisplaysChangedMetric();
 }
 
 void ChromeBrowserMainExtraPartsMetrics::OnDisplayRemoved(
     const display::Display& old_display) {
   EmitDisplaysChangedMetric();
@@ skipping 11 matching lines @@
   }
 }
 
 namespace chrome {
 
 void AddMetricsExtraParts(ChromeBrowserMainParts* main_parts) {
   main_parts->AddParts(new ChromeBrowserMainExtraPartsMetrics());
 }
 
 }  // namespace chrome