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 5d86799f5bcbea9d94fb8fed35df03154e15560f..932f3f6c477b9ddd436ceaef02ebf5ef75e05dd0 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',