Send traffic-management headers from extension updater.

chrome/browser/chromeos/extensions/external_cache.cc

Index: chrome/browser/chromeos/extensions/external_cache.cc
diff --git a/chrome/browser/chromeos/extensions/external_cache.cc b/chrome/browser/chromeos/extensions/external_cache.cc
index 52455ea5ba7af57ca6a90bdae0ca57fdad0618c4..65788fef69d21781f5934794b3c305a97255a94f 100644
--- a/chrome/browser/chromeos/extensions/external_cache.cc
+++ b/chrome/browser/chromeos/extensions/external_cache.cc
@@ -257,7 +257,9 @@ void ExternalCache::CheckCache() {
         update_url = extension_urls::GetWebstoreUpdateUrl();
 
       if (update_url.is_valid())
-        downloader_->AddPendingExtension(it.key(), update_url, false, 0);
+        downloader_->AddPendingExtension(
+            it.key(), update_url, false, 0,
+            extensions::ManifestFetchData::FetchPriority::BACKGROUND);
     }
 
     base::FilePath file_path;