Destroy DeviceImpl when the underlying UsbDevice is disconnected.

device/usb/mock_usb_device.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_USB_MOCK_USB_DEVICE_H_
 #define DEVICE_USB_MOCK_USB_DEVICE_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 25 matching lines @@
   MockUsbDevice(uint16_t vendor_id,
                 uint16_t product_id,
                 const std::string& manufacturer_string,
                 const std::string& product_string,
                 const std::string& serial_number,
                 const std::vector<UsbConfigDescriptor>& configurations);
 
   MOCK_METHOD1(Open, void(const OpenCallback&));
   MOCK_METHOD0(GetActiveConfiguration, const device::UsbConfigDescriptor*());
 
+  // Public wrapper around UsbDevice::NotifyDeviceRemoved().
+  void NotifyDeviceRemoved();
+
  private:
   ~MockUsbDevice() override;
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_MOCK_USB_DEVICE_H_