Add browser tests for USB device add/remove events.

device/usb/usb_service.h

 // Copyright 2014 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_USB_USB_SERVICE_H_
 #define DEVICE_USB_USB_SERVICE_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 37 matching lines @@
 
   // Get all of the devices attached to the system, inserting them into
   // |devices|. Clears |devices| before use. The result will be sorted by id
   // in increasing order.
   virtual void GetDevices(std::vector<scoped_refptr<UsbDevice> >* devices) = 0;
 
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);
 
  protected:
-  friend struct base::DefaultDeleter<UsbService>;
-
   UsbService();
   virtual ~UsbService();
 
   void NotifyDeviceAdded(scoped_refptr<UsbDevice> device);
   void NotifyDeviceRemoved(scoped_refptr<UsbDevice> device);
 
   ObserverList<Observer, true> observer_list_;
 
+ private:
+  class Destroyer;
+
   DISALLOW_COPY_AND_ASSIGN(UsbService);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_SERVICE_H_