Destroy DeviceImpl when the underlying UsbDevice is disconnected.

device/usb/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/usb_device.h"
 
 #include "base/guid.h"
 #include "device/usb/webusb_descriptors.h"
 
 namespace device {
 
+UsbDevice::Observer::~Observer() {}
+
+void UsbDevice::Observer::OnDeviceRemoved(scoped_refptr<UsbDevice> device) {}
+
 UsbDevice::UsbDevice(uint16_t vendor_id,
                      uint16_t product_id,
                      const base::string16& manufacturer_string,
                      const base::string16& product_string,
                      const base::string16& serial_number)
     : manufacturer_string_(manufacturer_string),
       product_string_(product_string),
       serial_number_(serial_number),
       guid_(base::GenerateGUID()),
       vendor_id_(vendor_id),
       product_id_(product_id) {}
 
 UsbDevice::~UsbDevice() {
 }
 
 void UsbDevice::CheckUsbAccess(const ResultCallback& callback) {
   // By default assume that access to the device is allowed. This is implemented
   // on Chrome OS by checking with permission_broker.
   callback.Run(true);
 }
 
+void UsbDevice::AddObserver(Observer* observer) {
+  observer_list_.AddObserver(observer);
+}
+
+void UsbDevice::RemoveObserver(Observer* observer) {
+  observer_list_.RemoveObserver(observer);
+}
+
+void UsbDevice::NotifyDeviceRemoved() {
+  FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemoved(this));
+}
+
 }  // namespace device