Introduce ServiceWorkerHandle for tracking WebServiceWorkerImpl reference

content/browser/service_worker/service_worker_context_core.cc

Index: content/browser/service_worker/service_worker_context_core.cc
diff --git a/content/browser/service_worker/service_worker_context_core.cc b/content/browser/service_worker/service_worker_context_core.cc
index c49d25be35047ef7875d5d5b16e0d48f8543218a..29f63655fae4f7ccf18313a3e4ebd04e91f800df 100644
--- a/content/browser/service_worker/service_worker_context_core.cc
+++ b/content/browser/service_worker/service_worker_context_core.cc
@@ -110,9 +110,8 @@ void ServiceWorkerContextCore::RegistrationComplete(
     return;
   }
 
-  DCHECK(version->registration());
   callback.Run(status,
-               version->registration()->id(),
+               version->registration_id(),
                version->version_id());
 }