BackgroundFetchRegistration.abort() should return a Promise.

content/browser/background_fetch/background_fetch_service_impl.cc

Index: content/browser/background_fetch/background_fetch_service_impl.cc
diff --git a/content/browser/background_fetch/background_fetch_service_impl.cc b/content/browser/background_fetch/background_fetch_service_impl.cc
index cb81edcaec3b54a7a3f1b5c15cf2f02796eb9a78..d9238374d0fdfe5fd81c54aa0dd9e4c3372917a6 100644
--- a/content/browser/background_fetch/background_fetch_service_impl.cc
+++ b/content/browser/background_fetch/background_fetch_service_impl.cc
@@ -50,11 +50,14 @@ void BackgroundFetchServiceImpl::UpdateUI(
 }
 
 void BackgroundFetchServiceImpl::Abort(int64_t service_worker_registration_id,
-                                       const std::string& tag) {
+                                       const std::string& tag,
+                                       const AbortCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
   // TODO(peter): Get the BackgroundFetchJobController for the
   // {service_worker_registration_id, tag} pair and call Abort() on it.
+
+  callback.Run(blink::mojom::BackgroundFetchError::NONE);
 }
 
 void BackgroundFetchServiceImpl::GetRegistration(