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

device/devices_app/devices_app.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_DEVICES_APP_H_
 #define DEVICE_DEVICES_DEVICES_APP_H_
 
 #include "base/cancelable_callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "mojo/application/public/cpp/application_delegate.h"
 #include "mojo/application/public/cpp/interface_factory.h"
 
+namespace base {
+class SequencedTaskRunner;
+}
+
 namespace mojo {
 class ApplicationImpl;
 }
 
 namespace device {
 
 namespace usb {
 class DeviceManager;
 }
 
 class DevicesApp : public mojo::ApplicationDelegate,
                    public mojo::InterfaceFactory<usb::DeviceManager> {
  public:
-  DevicesApp();
+  explicit DevicesApp(
+      scoped_refptr<base::SequencedTaskRunner> service_task_runner);
   ~DevicesApp() override;
 
  private:
   class USBServiceInitializer;
 
   // mojo::ApplicationDelegate:
   void Initialize(mojo::ApplicationImpl* app) override;
   bool ConfigureIncomingConnection(
       mojo::ApplicationConnection* connection) override;
   void Quit() override;
 
   // mojo::InterfaceFactory<usb::DeviceManager>:
   void Create(mojo::ApplicationConnection* connection,
               mojo::InterfaceRequest<usb::DeviceManager> request) override;
 
   // Mojo error handler to track device manager count.
   void OnConnectionError();
 
   // Sets the app for destruction after a period of idle time. If any top-level
   // services (e.g. usb::DeviceManager) are bound before the timeout elapses,
   // it's canceled.
   void StartIdleTimer();
 
   mojo::ApplicationImpl* app_impl_;
   scoped_ptr<USBServiceInitializer> service_initializer_;
+  scoped_refptr<base::SequencedTaskRunner> service_task_runner_;
   size_t active_device_manager_count_;
 
   // Callback used to shut down the app after a period of inactivity.
   base::CancelableClosure idle_timeout_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(DevicesApp);
 };
 
 }  // naespace device
 
 #endif  // DEVICE_DEVICES_DEVICES_APP_H_