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

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

Index: third_party/WebKit/Source/core/clipboard/DataTransfer.h
diff --git a/third_party/WebKit/Source/core/clipboard/DataTransfer.h b/third_party/WebKit/Source/core/clipboard/DataTransfer.h
index 18a2b2f3f3db0858372f5702a2204401109d4176..f8584f49eac642ec3ae17c251ac22c74204e7dab 100644
--- a/third_party/WebKit/Source/core/clipboard/DataTransfer.h
+++ b/third_party/WebKit/Source/core/clipboard/DataTransfer.h
@@ -87,7 +87,9 @@ class CORE_EXPORT DataTransfer final
   String getData(const String& type) const;
   void setData(const String& type, const String& data);
 
-  // extensions beyond IE's API
+  // Used by the bindings code to determine whether to call types() again.
+  bool hasDataStoreItemListChanged();
+
   Vector<String> types() const;
   FileList* files() const;
 
@@ -146,6 +148,8 @@ class CORE_EXPORT DataTransfer final
   DataTransferType transfer_type_;
   Member<DataObject> data_object_;
 
+  bool data_store_item_list_changed_;
+
   IntPoint drag_loc_;
   Member<ImageResourceContent> drag_image_;
   Member<Node> drag_image_element_;