Close USB device connections when the page is hidden.

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

 'use strict';
 
+function assertRejectsWithError(promise, name, message) {
+  return promise.then(() => {
+    assert_unreached('expected promise to reject with ' + name);
+  }, error => {
+    assert_equals(error.name, name);
+    if (message !== undefined)
+      assert_equals(error.message, message);
+  });
+}
+
 // TODO(reillyg): Remove when jyasskin upstreams this to testharness.js:
 // https://crbug.com/509058.
 function callWithKeyDown(functionCalledOnKeyPress) {
   return new Promise(resolve => {
     function onKeyPress() {
       document.removeEventListener('keypress', onKeyPress, false);
       resolve(functionCalledOnKeyPress());
     }
     document.addEventListener('keypress', onKeyPress, false);
 
@@ skipping 435 matching lines @@
 }
 
 function usb_test(func, name, properties) {
   mojo_test(mojo => usbMocks(mojo).then(usb => {
     let result = Promise.resolve(func(usb));
     let cleanUp = () => usb.mockDeviceManager.reset();
     result.then(cleanUp, cleanUp);
     return result;
   }), name, properties);
 }