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

chrome/test/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 1577 matching lines @@
       "../browser/media/wv_test_license_server_config.cc",
       "../browser/media/wv_test_license_server_config.h",
       "../browser/media_galleries/fileapi/iapps_finder_impl_win_browsertest.cc",
       "../browser/media_galleries/fileapi/media_file_validator_browsertest.cc",
       "../browser/media_galleries/media_galleries_dialog_controller_mock.cc",
       "../browser/media_galleries/media_galleries_dialog_controller_mock.h",
       "../browser/memory/tab_manager_browsertest.cc",
       "../browser/memory/tab_manager_observer_browsertest.cc",
       "../browser/metrics/metrics_memory_details_browsertest.cc",
       "../browser/metrics/metrics_service_browsertest.cc",
+      "../browser/metrics/tab_reactivation_tracker_browsertest.cc",
       "../browser/net/cookie_policy_browsertest.cc",
       "../browser/net/dns_probe_browsertest.cc",
       "../browser/net/errorpage_browsertest.cc",
       "../browser/net/ftp_browsertest.cc",
       "../browser/net/load_timing_browsertest.cc",
       "../browser/net/nqe/ui_network_quality_estimator_service_browsertest.cc",
       "../browser/net/nqe/ui_network_quality_estimator_service_test_util.cc",
       "../browser/net/nqe/ui_network_quality_estimator_service_test_util.h",
       "../browser/net/nss_context_chromeos_browsertest.cc",
       "../browser/net/predictor_browsertest.cc",
@@ skipping 3389 matching lines @@
       "touch_hud",
       "ui",
     ]
 
     if (is_linux && !is_android) {
       deps += [ "//components/font_service:manifest" ]
       packaged_services += [ "font_service" ]
     }
   }
 }