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

third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js

Index: third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js
diff --git a/third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js b/third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js
index 0ec82916bf90d4e1709cd26e63e628d8271c8895..e09689176419a9eb55bef72671bf342733348c92 100644
--- a/third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js
+++ b/third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js
@@ -13,6 +13,25 @@ function usb_test(func, name, properties) {
   }, name, properties);
 }
 
+// Returns a promise that is resolved when the next USBConnectionEvent of the
+// given type is received.
+function connectionEventPromise(eventType) {
+  return new Promise(resolve => {
+    let eventHandler = e => {
+      assert_true(e instanceof USBConnectionEvent);
+      navigator.usb.removeEventListener(eventType, eventHandler);
+      resolve(e.device);
+    };
+    navigator.usb.addEventListener(eventType, eventHandler);
+  });
+}
+
+function getConnectedDevice(deviceInit) {

[ortuno, 2017/04/12 03:31:07]

Comment what the function does.

Optional: You might want to change the name of the function it's not really
obvious what it does from reading a test.

[Reilly Grant (use Gerrit), 2017/04/12 22:47:07]

Done.

+  let promise = connectionEventPromise('connect');
+  navigator.usb.test.addFakeDevice(deviceInit);
+  return promise;
+}
+
 function assertRejectsWithError(promise, name, message) {
   return promise.then(() => {
     assert_unreached('expected promise to reject with ' + name);