Clone form data after dispatching the formdata event

Tests: web-platform-tests/wpt#14814.

source

@@ -56368,7 +56368,7 @@ fur
 
    <li><p>Set <var>form</var>'s <span>constructing entry list</span> to false.</p></li>
 
-   <li><p>Return <var>entry list</var>.</p></li>
+   <li><p>Return a <span data-x="list clone">clone</span> of <var>entry list</var>.</p></li>
   </ol>
 
   <p>To <dfn>append an entry</dfn> to <var>entry list</var>, given <var>name</var>,
@@ -56568,7 +56568,7 @@ fur
   <h5>The <code>FormDataEvent</code> interface</h5>
 
   <pre><code class="idl" data-x="">[Exposed=Window,
- Constructor(DOMString type, optional FormDataEventInit eventInitDict)]
+ Constructor(DOMString type, optional <span>FormDataEventInit</span> eventInitDict)]
 interface <dfn>FormDataEvent</dfn> : <span>Event</span> {
   readonly attribute <span>FormData</span> <span data-x="dom-FormDataEvent-formData">formData</span>;
 };