Fixing Indexed DB from latest Blink roll

tools/dom/idl/dart/dart.idl

 // This file introduces / supplements and forces Dart declarations.
 
 [Supplemental,
  Constructor]
 interface AudioContext {
   // TODO(ager): Auto-generate this custom method when the info about retaining
   // typed arrays is in the IDL.
   [Custom] void decodeAudioData(ArrayBuffer audioData, AudioBufferCallback successCallback, AudioBufferCallback errorCallback);
 };
 
@@ skipping 165 matching lines @@
   [Suppressed, StrictTypeChecking, Custom] void getVertexAttrib();
 };
 
 // TODO(vsm): Define new names for these (see b/4436830).
 [Supplemental]
 interface IDBCursor {
   [DartName=next, CallWith=ScriptExecutionContext, ImplementedAs=continueFunction, RaisesException] void continue([ForceOptional] optional any key);
 };
 [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);
 };
 
 [Supplemental]
 interface HTMLMediaElement {
   DOMString canPlayType([Default=Undefined] optional DOMString type, [Default=Undefined, TreatNullAs=NullString, TreatUndefinedAs=NullString, ForceOptional] optional DOMString keySystem);
 };
 
 [Supplemental]
@@ skipping 141 matching lines @@
 // TextEncoder/TextDecoder
 [Suppressed]
 interface TextEncoder {};
 
 [Suppressed]
 interface TextDecoder {};
 
 [Supplemental]
 interface Window : EventTarget {};