TreatReturnedNullStringAs=undefined removed from DataTransfer.idl

Source/core/clipboard/DataTransfer.idl

 /*
  * Copyright (C) 2008 Apple 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 13 matching lines @@
  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://html.spec.whatwg.org/#the-datatransfer-interface
 
 [
     GarbageCollected
 ] interface DataTransfer {
-    // TODO(philipj): Remove [TreatReturnedNullStringAs=Undefined].
-    [TreatReturnedNullStringAs=Undefined] attribute DOMString dropEffect;
-    [TreatReturnedNullStringAs=Undefined] attribute DOMString effectAllowed;
+    attribute DOMString dropEffect;
+    attribute DOMString effectAllowed;
 
     [SameObject] readonly attribute DataTransferItemList items;
 
     [RaisesException] void setDragImage(Element image, long x, long y);
 
     /* old interface */
     [SameObject] readonly attribute DOMString[] types;
     DOMString getData(DOMString format);
     void setData(DOMString format, DOMString data);
     void clearData(optional DOMString format);
     [SameObject] readonly attribute FileList files;
 };