Use IDL argument default values in modules/indexeddb/

Source/modules/indexeddb/IDBObjectStore.idl

Index: Source/modules/indexeddb/IDBObjectStore.idl
diff --git a/Source/modules/indexeddb/IDBObjectStore.idl b/Source/modules/indexeddb/IDBObjectStore.idl
index 14bd1daf49cd17faa3e07ec659470d0250578e4c..afffa8bc2a754f64429b238380020f7087adffd4 100644
--- a/Source/modules/indexeddb/IDBObjectStore.idl
+++ b/Source/modules/indexeddb/IDBObjectStore.idl
@@ -39,8 +39,8 @@
     [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);