Make new WebUSB implementation more resilient to garbage collection.

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 901719b9512e541a58b0d9b5dc518063a9bd301f..b3eff3a324081eed77b6a41ff3075e7a0ea0aa8c 100644
--- a/third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js
+++ b/third_party/WebKit/LayoutTests/usb/resources/usb-helpers.js
@@ -24,6 +24,14 @@ function callWithKeyDown(functionCalledOnKeyPress) {
   });
 }
 
+function runGarbageCollection() {
+  // Run gc() as a promise.
+  return new Promise((resolve, reject) => {
+    GCController.collect();
+    setTimeout(resolve, 0);
+  });
+}
+
 function usbMocks(mojo) {
   return define('USB Mocks', [
     'device/usb/public/interfaces/chooser_service.mojom',