Populate .current when navigator.serviceWorker is accessed

content/browser/service_worker/service_worker_handle.h

Index: content/browser/service_worker/service_worker_handle.h
diff --git a/content/browser/service_worker/service_worker_handle.h b/content/browser/service_worker/service_worker_handle.h
index 2aa7cc026f93aa6d331fe86fc6b1969d75be4b29..81d5b3574a242c62534508c2b2ed0764a58b5516 100644
--- a/content/browser/service_worker/service_worker_handle.h
+++ b/content/browser/service_worker/service_worker_handle.h
@@ -71,11 +71,16 @@ class CONTENT_EXPORT ServiceWorkerHandle
   ServiceWorkerVersion* version() { return version_.get(); }
   int handle_id() const { return handle_id_; }
 
+  bool HasNoRefCount() const { return ref_count_ <= 0; }
+  void IncrementRefCount();
+  void DecrementRefCount();
+
  private:
   base::WeakPtr<ServiceWorkerContextCore> context_;
   IPC::Sender* sender_;  // Not owned, it should always outlive this.
   const int thread_id_;
   const int handle_id_;
+  int ref_count_;  // Created with 1.
   scoped_refptr<ServiceWorkerRegistration> registration_;
   scoped_refptr<ServiceWorkerVersion> version_;