Ensure tests don't depend on fake devices being added synchronously

third_party/WebKit/LayoutTests/usb/resources/webusb-test.js

 'use strict';
 
 // This polyfil library implements the following WebIDL:
 //
 // partial interface USB {
 //   [SameObject] readonly attribute USBTest test;
 // }
 //
 // interface USBTest {
 //   attribute EventHandler ondeviceclose;
@@ skipping 58 matching lines @@
 // The global mojo object contains the Mojo JS binding modules loaded during
 // initialization.
 let mojo = null;
 
 // These variables are logically members of the USBTest class but are defined
 // here to hide them from being visible as fields of navigator.usb.test.
 let g_initializePromise = null;
 let g_chooserService = null;
 let g_deviceManager = null;
 let g_closeListener = null;
+let g_nextGuid = 0;
 
 function fakeDeviceInitToDeviceInfo(guid, init) {
   let deviceInfo = {
     guid: guid + "",
     usb_version_major: init.usbVersionMajor,
     usb_version_minor: init.usbVersionMinor,
     usb_version_subminor: init.usbVersionSubminor,
     class_code: init.deviceClass,
     subclass_code: init.deviceSubclass,
     protocol_code: init.deviceProtocol,
@@ skipping 262 matching lines @@
     this.bindingSet_ =
         new mojo.bindings.BindingSet(mojo.deviceManager.DeviceManager);
     this.devices_ = new Map();
     this.client_ = null;
   }
 
   addBinding(handle) {
     this.bindingSet_.addBinding(this, handle);
   }
 
-  addDevice(info) {
+  addDevice(guid, info) {
     let device = {
-      guid: this.nextGuid_++ + "",
+      guid: guid,
       info: info,
       bindingArray: []
     };
     this.devices_.set(device.guid, device);
     if (this.client_)
       this.client_.onDeviceAdded(fakeDeviceInitToDeviceInfo(device.guid, info));
-    return device.guid;
   }
 
   removeDevice(guid) {
     let device = this.devices_.get(guid);
+    if (!device)
+      throw new Error('Cannot remove unknown device "' + guid + '"');
+
     for (var binding of device.bindingArray)
       binding.close();
     this.devices_.delete(guid);
     if (this.client_) {
       this.client_.onDeviceRemoved(
           fakeDeviceInitToDeviceInfo(guid, device.info));
     }
   }
 
   removeAllDevices() {
@@ skipping 134 matching lines @@
             handle => g_chooserService.addBinding(handle));
         resolve();
       });
     });
   }
 
   addFakeDevice(deviceInit) {
     if (!g_deviceManager)
       throw new Error('Call initialize() before addFakeDevice().');
 
-    return g_deviceManager.addDevice(deviceInit);
+    // |addDevice| and |removeDevice| are called in a setTimeout callback so
+    // that tests do not rely on the device being immediately available which
+    // may not be true for all implementations of this test API.
+    let guid = (g_nextGuid++).toString();
+    setTimeout(() => g_deviceManager.addDevice(guid, deviceInit), 0);
+    return guid;
   }
 
   removeFakeDevice(guid) {
     if (!g_deviceManager)
       throw new Error('Call initialize() before removeFakeDevice().');
 
-    return g_deviceManager.removeDevice(guid);
+    setTimeout(() => g_deviceManager.removeDevice(guid), 0);
   }
 
   set ondeviceclose(func) {
     g_closeListener = func;
   }
 
   set chosenDevice(guid) {
     if (!g_chooserService)
       throw new Error('Call initialize() before setting chosenDevice.');
 
@@ skipping 13 matching lines @@
 
     g_deviceManager.removeAllDevices();
     g_chooserService.setChosenDevice(null);
     g_closeListener = null;
   }
 }
 
 navigator.usb.test = new USBTest();
 
 })();