Migrate Extensions code to Task Scheduler API

extensions/browser/api/storage/backend_task_runner.h

Index: extensions/browser/api/storage/backend_task_runner.h
diff --git a/extensions/browser/api/storage/backend_task_runner.h b/extensions/browser/api/storage/backend_task_runner.h
new file mode 100644
index 0000000000000000000000000000000000000000..d19f095e431c833dff65d3d9766812e8a6e46886
--- /dev/null
+++ b/extensions/browser/api/storage/backend_task_runner.h
@@ -0,0 +1,22 @@
+// 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 EXTENSIONS_BROWSER_API_STORAGE_BACKEND_TASK_RUNNER_H_
+#define EXTENSIONS_BROWSER_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 storage backend on.
+scoped_refptr<base::SequencedTaskRunner> GetBackendTaskRunner();
+
+// Verifies the the backend task runner above runs tasks in the current
+// sequence.
+bool IsOnBackendSequence();
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_API_STORAGE_BACKEND_TASK_RUNNER_H_