ServiceWorker: Ensure live registration during starting worker

content/browser/service_worker/service_worker_dispatcher_host.cc

Index: content/browser/service_worker/service_worker_dispatcher_host.cc
diff --git a/content/browser/service_worker/service_worker_dispatcher_host.cc b/content/browser/service_worker/service_worker_dispatcher_host.cc
index 317107ab6095c9e333cc1859fd235933167e5663..9629877d38362a0b01cc75c1354bb5905b602b0b 100644
--- a/content/browser/service_worker/service_worker_dispatcher_host.cc
+++ b/content/browser/service_worker/service_worker_dispatcher_host.cc
@@ -594,10 +594,12 @@ void ServiceWorkerDispatcherHost::OnSetHostedVersionId(
   if (!provider_host->SetHostedVersionId(version_id))
     BadMessageReceived();
 
-  // Retrieve the registration associated with |version_id|.
   ServiceWorkerVersion* version = GetContext()->GetLiveVersion(version_id);
   if (!version)
     return;
+
+  // Retrieve the registration associated with |version|. The registration
+  // must be alive because the version keeps it during starting worker.
   ServiceWorkerRegistration* registration =
       GetContext()->GetLiveRegistration(version->registration_id());
   DCHECK(registration);