Import Mozilla's IDBObjectStore.openKeyCursor() test

LayoutTests/storage/indexeddb/mozilla/resources/generator_test_adapter.js

 'use strict';
 
 // Adapter for Mozilla's getAll tests to Blink's js-test.
 
 var jsTestIsAsync = true;
 
 // Moz tests are still prefixed
 IDBObjectStore.prototype.mozGetAll = IDBObjectStore.prototype.getAll;
 IDBObjectStore.prototype.mozGetAllKeys = IDBObjectStore.prototype.getAllKeys;
 IDBIndex.prototype.mozGetAll = IDBIndex.prototype.getAll;
@@ skipping 13 matching lines @@
 }
 function is(a, b, message) {
     ok(Object.is(a, b), message);
 }
 function grabEventAndContinueHandler(e) {
     testGenerator.next(e);
 }
 function executeSoon(f) {
     setTimeout(f, 0);
 }
+function continueToNextStepSync() {
+    testGenerator.next();
+}
 function finishTest() {
     finishJSTest();
 }
 function unexpectedSuccessHandler(e) {
     ok(false, "Unexpected success");
 }
 function info(message) {
     debug(message);
 }
 testGenerator.next();