Use IDL argument default values in modules/indexeddb/

Source/modules/indexeddb/IDBObjectStore.idl

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 21 matching lines @@
     [CallWith=ScriptState] readonly attribute any keyPath;
     readonly attribute DOMStringList indexNames;
     readonly attribute IDBTransaction transaction;
     readonly attribute boolean autoIncrement;
 
     [CallWith=ScriptState, RaisesException] IDBRequest put(any value, [Default=Undefined] optional any key);
     [CallWith=ScriptState, RaisesException] IDBRequest add(any value, [Default=Undefined] optional any key);
     [CallWith=ScriptState, ImplementedAs=deleteFunction, RaisesException] IDBRequest delete(any key);
     [CallWith=ScriptState, RaisesException] IDBRequest get(any key);
     [CallWith=ScriptState, RaisesException] IDBRequest clear();
-    [CallWith=ScriptState, RaisesException] IDBRequest openCursor([Default=Undefined] optional any range, optional DOMString direction = null);
-    [CallWith=ScriptState, RaisesException, RuntimeEnabled=IndexedDBExperimental] IDBRequest openKeyCursor([Default=Undefined] optional any range, optional DOMString direction = null);
+    [CallWith=ScriptState, RaisesException] IDBRequest openCursor([Default=Undefined] optional any range, optional DOMString direction = "next");
+    [CallWith=ScriptState, RaisesException, RuntimeEnabled=IndexedDBExperimental] IDBRequest openKeyCursor([Default=Undefined] optional any range, optional DOMString direction = "next");
     // FIXME: should be union type http://crbug.com/240176
     [CallWith=ScriptState, RaisesException] IDBIndex createIndex(DOMString name, DOMString keyPath, optional Dictionary options);
     [CallWith=ScriptState, RaisesException] IDBIndex createIndex(DOMString name, sequence<DOMString> keyPath, optional Dictionary options);
     [RaisesException] IDBIndex index(DOMString name);
     [RaisesException] void deleteIndex(DOMString name);
     [CallWith=ScriptState, RaisesException] IDBRequest count([Default=Undefined] optional any key);
 };