Destroy DeviceImpl when the underlying UsbDevice is disconnected.

device/usb/mock_usb_device.cc

 // 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 "device/usb/mock_usb_device.h"
 
 #include "base/strings/utf_string_conversions.h"
 
 namespace device {
 
@@ skipping 43 matching lines @@
                     product_id,
                     manufacturer_string,
                     product_string,
                     serial_number) {
   configurations_ = configurations;
 }
 
 MockUsbDevice::~MockUsbDevice() {
 }
 
+void MockUsbDevice::NotifyDeviceRemoved() {
+  UsbDevice::NotifyDeviceRemoved();
+}
+
 }  // namespace device