Migrate WebUSB LayoutTests into external/wpt

third_party/WebKit/LayoutTests/external/wpt_automation/webusb/webusb-test.js

 'use strict';
 
 // This polyfil library implements the following WebIDL:

[foolip, 2017/04/05 06:03:32]

Is this test API included in some spec? It's not in
https://wicg.github.io/webusb/ itself.

[Reilly Grant (use Gerrit), 2017/04/05 18:39:37]

This test API is not yet included in any spec. The purpose of this patch is to
prove out the concept of polyfilling this kind of test API. If people approve I
will go write the spec. It would be similar to,

https://webbluetoothcg.github.io/web-bluetooth/tests

 //
 // partial interface USB {
 //   [SameObject] readonly attribute USBTest test;
 // }
 //
 // interface USBTest {
 //   attribute EventHandler ondeviceclose;
 //   attribute DOMString? chosenDevice;
 //   attribute FrozenArray<USBDeviceFilter>? lastFilters;
 //
@@ skipping 542 matching lines @@
 
     g_deviceManager.removeAllDevices();
     g_chooserService.setChosenDevice(null);
     g_closeListener = null;
   }
 }
 
 navigator.usb.test = new USBTest();
 
 })();