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

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc

Index: chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
diff --git a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
index b1af95d46c49e1f16df919098bf4be74ca4560cc..62577e52df9289e609c5e933c2478d707f6e5989 100644
--- a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
+++ b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
@@ -21,6 +21,7 @@
 #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"
@@ -370,6 +371,8 @@ void ChromeBrowserMainExtraPartsMetrics::PostBrowserStart() {
 #if !defined(OS_ANDROID)
   FirstWebContentsProfiler::Start();
 #endif  // !defined(OS_ANDROID)
+
+  metrics::TabUsageRecorder::Initialize();
 }
 
 void ChromeBrowserMainExtraPartsMetrics::OnDisplayAdded(