[Extensions] Convert APIs to use movable types [4]

chrome/common/extensions/api/downloads_internal.idl

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // downloadsInternal
-[nodoc=true]
+[nodoc=true,use_movable_types=true]
 namespace downloadsInternal {
   interface Functions {
     // Secretly called when onDeterminingFilename handlers return.
     static void determineFilename(long downloadId,
                                   DOMString filename,
                                   DOMString conflict_action);
   };
 };