Add device path enumeration to the new Windows USB backend.

device/usb/usb_device.h

Index: device/usb/usb_device.h
diff --git a/device/usb/usb_device.h b/device/usb/usb_device.h
index bf16d03ac5d5d6737f0d24cd6f9d4c2c562c9de5..870a29ab9c2b37a3bf3f5923e6ab662dff64e977 100644
--- a/device/usb/usb_device.h
+++ b/device/usb/usb_device.h
@@ -96,6 +96,7 @@ class UsbDevice : public base::RefCountedThreadSafe<UsbDevice> {
  protected:
   friend class UsbService;
 
+  UsbDevice();
   UsbDevice(uint16_t usb_version,
             uint8_t device_class,
             uint8_t device_subclass,
@@ -134,6 +135,7 @@ class UsbDevice : public base::RefCountedThreadSafe<UsbDevice> {
   friend class UsbServiceAndroid;
   friend class UsbServiceImpl;
   friend class UsbServiceLinux;
+  friend class UsbServiceWin;
 
   void OnDisconnect();
   void HandleClosed(UsbDeviceHandle* handle);