Migrate Extensions code to Task Scheduler API

chrome/browser/extensions/api/storage/backend_task_runner.h

Index: chrome/browser/extensions/api/storage/backend_task_runner.h
diff --git a/chrome/browser/extensions/api/storage/backend_task_runner.h b/chrome/browser/extensions/api/storage/backend_task_runner.h
deleted file mode 100644
index 50c60e08d063ee11435562ed596b64a106e40811..0000000000000000000000000000000000000000
--- a/chrome/browser/extensions/api/storage/backend_task_runner.h
+++ /dev/null
@@ -1,18 +0,0 @@
-// 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 CHROME_BROWSER_EXTENSIONS_API_STORAGE_BACKEND_TASK_RUNNER_H_
-#define CHROME_BROWSER_EXTENSIONS_API_STORAGE_BACKEND_TASK_RUNNER_H_
-
-#include "base/memory/ref_counted.h"
-#include "base/sequenced_task_runner.h"
-
-namespace extensions {
-
-// Gets the singleton task runner for running SyncStorageBackend on.
-scoped_refptr<base::SequencedTaskRunner> GetBackendTaskRunner();
-
-}  // namespace extensions
-
-#endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_BACKEND_TASK_RUNNER_H_