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

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

Index: third_party/WebKit/LayoutTests/usb/resources/webusb-test.js
diff --git a/third_party/WebKit/LayoutTests/usb/resources/webusb-test.js b/third_party/WebKit/LayoutTests/usb/resources/webusb-test.js
index 2af2182cb3debc780fad8e2dfbd0aeeb8dcbc626..cc0a64db0caf92076ece9ad30c78101b8f8ea95b 100644
--- a/third_party/WebKit/LayoutTests/usb/resources/webusb-test.js
+++ b/third_party/WebKit/LayoutTests/usb/resources/webusb-test.js
@@ -76,6 +76,7 @@ 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 = {
@@ -358,20 +359,22 @@ class FakeDeviceManager {
     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);
@@ -526,14 +529,19 @@ class USBTest {
     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) {