Use the task scheduler in the new Windows USB backend

device/test/test_device_client.h

 // Copyright 2015 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.
 
 #include <memory>
 
-#include "base/memory/ref_counted.h"
 #include "device/base/device_client.h"
 
-namespace base {
-class SingleThreadTaskRunner;
-}
-
 namespace device {
 
 class HidService;
 class UsbService;
 
 class TestDeviceClient : public DeviceClient {
  public:
-  TestDeviceClient(scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  TestDeviceClient();
 
   // Must be destroyed when tasks can still be posted to |task_runner|.
   ~TestDeviceClient() override;
 
   HidService* GetHidService() override;
   UsbService* GetUsbService() override;
 
  private:
   std::unique_ptr<HidService> hid_service_;
   std::unique_ptr<UsbService> usb_service_;
-  scoped_refptr<base::SingleThreadTaskRunner> blocking_task_runner_;
 };
 
 }  // namespace device