DataTransfer: Make |types| be a FrozenArray<DOMString>.

third_party/WebKit/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 21 matching lines @@
     Constructor,
 ] interface DataTransfer {
     attribute DOMString dropEffect;
     attribute DOMString effectAllowed;
 
     [SameObject] readonly attribute DataTransferItemList items;
 
     void setDragImage(Element image, long x, long y);
 
     /* old interface */
-    // TODO(foolip): Switch to FrozenArray<DOMString> when the spec is fixed:
-    // https://github.com/whatwg/html/issues/11
-    [SameObject] readonly attribute DOMString[] types;
+    [CachedAttribute=hasDataStoreItemListChanged] readonly attribute FrozenArray<DOMString> types;
     DOMString getData(DOMString format);
     void setData(DOMString format, DOMString data);
     void clearData(optional DOMString format);
     [SameObject] readonly attribute FileList files;
 };