Mark VoidCallback as a [Callback]

client/dom/idl/dart/dart.idl

 
 // This file introduces / supplements and forces Dart declarations.
 
 module default {
   NamedNodeMap implements sequence<Node>;
   NodeList implements sequence<Node>;
   HTMLCollection implements sequence<Node>;
   MediaList implements sequence<DOMString>;
   StyleSheetList implements sequence<StyleSheet>;
   TouchList implements sequence<Touch>;
@@ skipping 152 matching lines @@
   };
   [Supplemental]
   interface IDBIndex {
     [DartName=getObject] IDBRequest get(in IDBKey key);
   };
   [Supplemental]
   interface IDBObjectStore {
     [DartName=getObject] IDBRequest get(in IDBKey key);
   };
 };
+
+module html {
+  [Supplemental, Callback] // Add missing Callback attribute.
+  interface VoidCallback {
+  };
+};
+