(Merge to M46) Fix crash with null ServiceWorkerProviderHost in DidDispatchFetchEvent

content/browser/service_worker/service_worker_url_request_job.cc

Index: content/browser/service_worker/service_worker_url_request_job.cc
diff --git a/content/browser/service_worker/service_worker_url_request_job.cc b/content/browser/service_worker/service_worker_url_request_job.cc
index 09ad63ecd6a6e06aa6d00fdc10ebab4d5ed3c688..2572c93a59b5ad3b7190b1cfa47dd3e383cf762f 100644
--- a/content/browser/service_worker/service_worker_url_request_job.cc
+++ b/content/browser/service_worker/service_worker_url_request_job.cc
@@ -589,6 +589,14 @@ void ServiceWorkerURLRequestJob::DidDispatchFetchEvent(
     return;
   }
 
+  // A null |provider_host_| probably means the tab was closed. The null value
+  // would cause problems down the line, so bail out.
+  if (!provider_host_) {
+    RecordResult(ServiceWorkerMetrics::REQUEST_JOB_ERROR_NO_PROVIDER_HOST);
+    DeliverErrorResponse();
+    return;
+  }
+
   if (status != SERVICE_WORKER_OK) {
     RecordResult(ServiceWorkerMetrics::REQUEST_JOB_ERROR_FETCH_EVENT_DISPATCH);
     if (is_main_resource_load_) {