Add UMA for how long service workers run for.

content/browser/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/features.gni")
 import("//build/config/ui.gni")
 import("//media/media_options.gni")
 import("//ppapi/features/features.gni")
 import("//printing/features/features.gni")
 import("//third_party/WebKit/public/public_features.gni")
@@ skipping 1249 matching lines @@
     "service_worker/service_worker_fetch_dispatcher.cc",
     "service_worker/service_worker_fetch_dispatcher.h",
     "service_worker/service_worker_handle.cc",
     "service_worker/service_worker_handle.h",
     "service_worker/service_worker_info.cc",
     "service_worker/service_worker_info.h",
     "service_worker/service_worker_internals_ui.cc",
     "service_worker/service_worker_internals_ui.h",
     "service_worker/service_worker_job_coordinator.cc",
     "service_worker/service_worker_job_coordinator.h",
+    "service_worker/service_worker_lifetime_tracker.cc",
+    "service_worker/service_worker_lifetime_tracker.h",
     "service_worker/service_worker_metrics.cc",
     "service_worker/service_worker_metrics.h",
     "service_worker/service_worker_navigation_handle.cc",
     "service_worker/service_worker_navigation_handle.h",
     "service_worker/service_worker_navigation_handle_core.cc",
     "service_worker/service_worker_navigation_handle_core.h",
     "service_worker/service_worker_process_manager.cc",
     "service_worker/service_worker_process_manager.h",
     "service_worker/service_worker_provider_host.cc",
     "service_worker/service_worker_provider_host.h",
@@ skipping 737 matching lines @@
   if (!is_component_build) {
     public_deps = [
       ":browser",
     ]
   } else {
     public_deps = [
       "//third_party/leveldatabase",
     ]
   }
 }