Provide the DeviceManager service to the renderer directly, no app.

device/devices_app/public/cpp/devices_app_factory.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.
 
 #ifndef DEVICE_DEVICES_APP_PUBLIC_CPP_DEVICES_APP_FACTORY_H_
 #define DEVICE_DEVICES_APP_PUBLIC_CPP_DEVICES_APP_FACTORY_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 
-namespace base {
-class SequencedTaskRunner;
-}
-
 namespace mojo {
 class ApplicationDelegate;
 }
 
 namespace device {
 
 // Public factory for creating new instances of the devices app.
 class DevicesAppFactory {
  public:
   // Creates a DevicesApp delegate which can be used to launch a new instance
   // of the devices app on a mojo application runner. The caller owns the
   // delegate.
-  //
-  // |service_task_runner| is the thread TaskRunner on which the UsbService
-  // lives. This argument should be removed once UsbService is owned by the
-  // USB device manager and no longer part of the public device API. If null,
-  // the app will construct its own DeviceClient and UsbService.
-  static scoped_ptr<mojo::ApplicationDelegate> CreateApp(
-      scoped_refptr<base::SequencedTaskRunner> service_task_runner);
+  static scoped_ptr<mojo::ApplicationDelegate> CreateApp();
 };
 
 }  // namespace device
 
 #endif  // DEVICE_DEVICES_APP_PUBLIC_CPP_DEVICES_APP_FACTORY_H_