BackgroundFetchRegistration.abort() should return a Promise.

content/browser/background_fetch/background_fetch_service_impl.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_BACKGROUND_FETCH_BACKGROUND_FETCH_SERVICE_IMPL_H_
 #define CONTENT_BROWSER_BACKGROUND_FETCH_BACKGROUND_FETCH_SERVICE_IMPL_H_
 
 #include <string>
 #include <utility>
 
@@ skipping 17 matching lines @@
       scoped_refptr<BackgroundFetchContext> background_fetch_context,
       scoped_refptr<ServiceWorkerContextWrapper> service_worker_context,
       blink::mojom::BackgroundFetchServiceRequest request);
 
   // blink::mojom::BackgroundFetchService implementation.
   void UpdateUI(int64_t service_worker_registration_id,
                 const std::string& tag,
                 const std::string& title,
                 const UpdateUICallback& callback) override;
   void Abort(int64_t service_worker_registration_id,
-             const std::string& tag) override;
+             const std::string& tag,
+             const AbortCallback& callback) override;
   void GetRegistration(int64_t service_worker_registration_id,
                        const std::string& tag,
                        const GetRegistrationCallback& callback) override;
   void GetTags(int64_t service_worker_registration_id,
                const GetTagsCallback& callback) override;
 
  private:
   scoped_refptr<BackgroundFetchContext> background_fetch_context_;
   scoped_refptr<ServiceWorkerContextWrapper> service_worker_context_;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundFetchServiceImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_BACKGROUND_FETCH_BACKGROUND_FETCH_SERVICE_IMPL_H_