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

third_party/WebKit/Source/core/clipboard/DataTransfer.idl

Index: third_party/WebKit/Source/core/clipboard/DataTransfer.idl
diff --git a/third_party/WebKit/Source/core/clipboard/DataTransfer.idl b/third_party/WebKit/Source/core/clipboard/DataTransfer.idl
index 71ab1f72c672d5f180e5a4c8277d7260dedf7d5b..6129bba0656ce773a0ccd3a9ba78e52276909a58 100644
--- a/third_party/WebKit/Source/core/clipboard/DataTransfer.idl
+++ b/third_party/WebKit/Source/core/clipboard/DataTransfer.idl
@@ -39,9 +39,7 @@
     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;
+    readonly attribute FrozenArray<DOMString> types;

[foolip, 2017/05/12 07:51:42]

This will require some tests, can you update
LayoutTests/external/wpt/html/editing/dnd/datastore/datatransfer-constructor-001.html?

LayoutTests/external/wpt/mediasession/mediametadata.html is an example of how to
use Object.isFrozen to test this.

Although you are not changing it here, can you also test
`assert_equals(transfer.types, transfer.types)`. I'm pretty sure that will fail,
and if you want to fix it at the same time, that'd be great. I think you'll need
to use [CachedAttribute=bla] here to fix it.

     DOMString getData(DOMString format);
     void setData(DOMString format, DOMString data);
     void clearData(optional DOMString format);