Reduce/remove usage of BrowserThread in content/browser/loader.

content/browser/service_worker/service_worker_fetch_dispatcher.cc

Index: content/browser/service_worker/service_worker_fetch_dispatcher.cc
diff --git a/content/browser/service_worker/service_worker_fetch_dispatcher.cc b/content/browser/service_worker/service_worker_fetch_dispatcher.cc
index 7017787fc0db354558c02f84c6423dbdc2aefdf5..e18d18415fab6aa62ecf9c55579e5da5008dbfbe 100644
--- a/content/browser/service_worker/service_worker_fetch_dispatcher.cc
+++ b/content/browser/service_worker/service_worker_fetch_dispatcher.cc
@@ -537,7 +537,8 @@ bool ServiceWorkerFetchDispatcher::MaybeStartNavigationPreload(
   mojom::URLLoaderFactoryPtr url_loader_factory;
   URLLoaderFactoryImpl::Create(
       ResourceRequesterInfo::CreateForNavigationPreload(requester_info),
-      mojo::MakeRequest(&url_loader_factory));
+      mojo::MakeRequest(&url_loader_factory),
+      BrowserThread::GetTaskRunnerForThread(BrowserThread::IO));
 
   ResourceRequest request;
   request.method = original_request->method();