ServiceWorker: Add null check in ServiceWorkerContextWrapper::DeleteAndStartOver

content/browser/service_worker/service_worker_context_wrapper.cc

Index: content/browser/service_worker/service_worker_context_wrapper.cc
diff --git a/content/browser/service_worker/service_worker_context_wrapper.cc b/content/browser/service_worker/service_worker_context_wrapper.cc
index 7d20899a9decb634ea2dcd10ea442f4fabeecbb6..8df6f4297a8cf06b966b6ef26caca543ecf9b0a0 100644
--- a/content/browser/service_worker/service_worker_context_wrapper.cc
+++ b/content/browser/service_worker/service_worker_context_wrapper.cc
@@ -143,6 +143,13 @@ void ServiceWorkerContextWrapper::Shutdown() {
 
 void ServiceWorkerContextWrapper::DeleteAndStartOver() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  if (!context_core_) {
+    // The context could be null due to system shutdown or restart failure. In
+    // either case, we should not have to recover the system, so just return
+    // here.
+    LOG(ERROR) << "ServiceWorkerContextCore is no longer alive.";
+    return;
+  }
   context_core_->DeleteAndStartOver(
       base::Bind(&ServiceWorkerContextWrapper::DidDeleteAndStartOver, this));
 }