Fixing Indexed DB from latest Blink roll

tools/dom/idl/dart/dart.idl

Index: tools/dom/idl/dart/dart.idl
diff --git a/tools/dom/idl/dart/dart.idl b/tools/dom/idl/dart/dart.idl
index a38ee947c87d403a3026622ad99ea1bac71ca045..ca2ccd05b92c5e0d7542e2dbfe91353392a222ed 100644
--- a/tools/dom/idl/dart/dart.idl
+++ b/tools/dom/idl/dart/dart.idl
@@ -183,9 +183,9 @@ interface IDBCursor {
 };
 [Supplemental]
 interface IDBIndex {
-    [CallWith=ScriptExecutionContext, RaisesException] IDBRequest openCursor([Default=Undefined] optional any key, [Default=NullString] optional DOMString direction);
+    [CallWith=ScriptExecutionContext, RaisesException] IDBRequest openCursor([Default=Undefined] optional any key, [ForceOptional] optional DOMString direction);
 
-    [CallWith=ScriptExecutionContext, RaisesException] IDBRequest openKeyCursor([Default=Undefined] optional any key, [Default=NullString] optional DOMString direction);
+    [CallWith=ScriptExecutionContext, RaisesException] IDBRequest openKeyCursor([Default=Undefined] optional any key, [ForceOptional] optional DOMString direction);
 
     [CallWith=ScriptExecutionContext, RaisesException] IDBRequest count([Default=Undefined] optional any key);
 };