Add UMA for how long service workers run for.

content/browser/service_worker/service_worker_context_core.h

Index: content/browser/service_worker/service_worker_context_core.h
diff --git a/content/browser/service_worker/service_worker_context_core.h b/content/browser/service_worker/service_worker_context_core.h
index bb1fc8993cc8fca8c8472648306c06ccd72031bb..c57eb9d7e1607b053fcde87574263375564e5a10 100644
--- a/content/browser/service_worker/service_worker_context_core.h
+++ b/content/browser/service_worker/service_worker_context_core.h
@@ -19,6 +19,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list_threadsafe.h"
 #include "content/browser/service_worker/service_worker_info.h"
+#include "content/browser/service_worker/service_worker_lifetime_tracker.h"
 #include "content/browser/service_worker/service_worker_process_manager.h"
 #include "content/browser/service_worker/service_worker_provider_host.h"
 #include "content/browser/service_worker/service_worker_registration_status.h"
@@ -144,6 +145,7 @@ class CONTENT_EXPORT ServiceWorkerContextCore
                          ServiceWorkerProviderHost* provider_host) override;
   void OnControlleeRemoved(ServiceWorkerVersion* version,
                            ServiceWorkerProviderHost* provider_host) override;
+  void OnDevToolsAttached(ServiceWorkerVersion* version) override;
 
   ServiceWorkerContextWrapper* wrapper() const { return wrapper_; }
   ServiceWorkerStorage* storage() { return storage_.get(); }
@@ -377,6 +379,8 @@ class CONTENT_EXPORT ServiceWorkerContextCore
   bool was_service_worker_registered_;
   scoped_refptr<base::ObserverListThreadSafe<ServiceWorkerContextObserver>>
       observer_list_;
+  ServiceWorkerLifetimeTracker lifetime_tracker_;
+
   base::WeakPtrFactory<ServiceWorkerContextCore> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ServiceWorkerContextCore);