IndexedDB: Array-type keypaths should not be returned as DOMStringLists

LayoutTests/storage/indexeddb/resources/keypath-arrays.js

 if (this.importScripts) {
     importScripts('../../../resources/js-test.js');
     importScripts('shared.js');
 }
 
 description("Test IndexedDB Array-type keyPaths");
 
 indexedDBTest(prepareDatabase, testKeyPaths);
 function prepareDatabase()
 {
     db = event.target.result;
     event.target.transaction.onabort = unexpectedAbortCallback;
     evalAndLog("store = db.createObjectStore('store', {keyPath: ['a', 'b']})");
-    evalAndLog("store.createIndex('index', ['c', 'd'])");
+    evalAndLog("index = store.createIndex('index', ['c', 'd'])");
+
+    shouldBeTrue("areArraysEqual(index.keyPath, ['c', 'd'])");
+    shouldBeFalse("index.keyPath instanceof DOMStringList");
 
     evalAndExpectException("db.createObjectStore('store-with-generator', {keyPath: ['a', 'b'], autoIncrement: true})", "DOMException.INVALID_ACCESS_ERR");
     evalAndExpectException("store.createIndex('index-multientry', ['e', 'f'], {multiEntry: true})", "DOMException.INVALID_ACCESS_ERR");
 
     debug("");
     debug("Empty arrays are not valid key paths:");
     evalAndExpectException("db.createObjectStore('store-keypath-empty-array', {keyPath: []})", "DOMException.SYNTAX_ERR");
     evalAndExpectException("store.createIndex('index-keypath-empty-array', [])", "DOMException.SYNTAX_ERR");
 }
 
@@ skipping 29 matching lines @@
         request.onsuccess = function () {
             evalAndLog("cursor = request.result");
             shouldBeNonNull("cursor");
             shouldBeEqualToString("JSON.stringify(cursor.primaryKey)", "[1,2]");
             shouldBeEqualToString("JSON.stringify(cursor.key)", "[3,4]");
         };
     };
 
     transaction.oncomplete = finishJSTest;
 }