Fix file scheme downloads back to work without RenderFrameHost

Fixes crrev.com/c/2337411 which inadvertently changed file scheme
downloads to only work when a RenderFrameHost exists.

Bug: 1106995
Change-Id: I9f87c6c2b1b8719e1c78b2aa670b02ff8ac65381
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2397041Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805070}

content/browser/download/download_manager_impl.cc

@@ -1289,6 +1289,15 @@ void DownloadManagerImpl::BeginResourceDownloadOnChecksComplete(
   if (blob_url_loader_factory) {
     DCHECK(params->url().SchemeIsBlob());
     pending_url_loader_factory = blob_url_loader_factory->Clone();
+  } else if (params->url().SchemeIsFile()) {
+    pending_url_loader_factory =
+        std::make_unique<network::WrapperPendingSharedURLLoaderFactory>(
+            FileURLLoaderFactory::Create(
+                browser_context_->GetPath(),
+                browser_context_->GetSharedCorsOriginAccessList(),
+                // USER_VISIBLE because download should progress
+                // even when there is high priority work to do.
+                base::TaskPriority::USER_VISIBLE));
   } else if (rfh && params->url().SchemeIs(content::kChromeUIScheme)) {
     mojo::PendingRemote<network::mojom::URLLoaderFactory>
         url_loader_factory_remote;
@@ -1323,15 +1332,6 @@ void DownloadManagerImpl::BeginResourceDownloadOnChecksComplete(
     ContentBrowserClient::NonNetworkURLLoaderFactoryMap
         non_network_url_loader_factories;
 
-    // USER_VISIBLE because download should progress
-    // even when there is high priority work to do.
-    base::TaskPriority file_factory_priority = base::TaskPriority::USER_VISIBLE;
-    non_network_url_loader_factories.emplace(
-        url::kFileScheme, FileURLLoaderFactory::Create(
-                              browser_context_->GetPath(),
-                              browser_context_->GetSharedCorsOriginAccessList(),
-                              file_factory_priority));
-
     GetContentClient()
         ->browser()
         ->RegisterNonNetworkSubresourceURLLoaderFactories(