Add a service to track devices selected by the user.

device/usb/usb_device_impl.cc

Index: device/usb/usb_device_impl.cc
diff --git a/device/usb/usb_device_impl.cc b/device/usb/usb_device_impl.cc
index 84f7143431b41fd3e0cef8808c054ac0cd711922..a9838dc6a08005519b9f3e5e82f239a78a3ab5bd 100644
--- a/device/usb/usb_device_impl.cc
+++ b/device/usb/usb_device_impl.cc
@@ -98,6 +98,17 @@ UsbUsageType GetUsageType(const libusb_endpoint_descriptor* descriptor) {
 
 }  // namespace
 
+UsbDevice::UsbDevice(uint16 vendor_id, uint16 product_id, uint32 unique_id)
+    : vendor_id_(vendor_id), product_id_(product_id), unique_id_(unique_id) {
+}
+
+UsbDevice::~UsbDevice() {
+}
+
+void UsbDevice::NotifyDisconnect() {
+  FOR_EACH_OBSERVER(Observer, observer_list_, OnDisconnect(this));
+}
+
 UsbDeviceImpl::UsbDeviceImpl(
     scoped_refptr<UsbContext> context,
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner,