Move chrome.downloads out of experimental to dev

chrome/common/extensions/api/experimental_serial.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.
 
-// File-level comment to appease parser. Eventually this will not be necessary.
-
 [nodoc] namespace experimental.serial {
 
   callback GetPortsCallback = void (DOMString[] ports);
 
   dictionary OpenInfo {
     // The id of the opened connection.
     long connectionId;
   };
 
   callback OpenCallback = void (OpenInfo openInfo);
@@ skipping 56 matching lines @@
                       WriteCallback callback);
 
     // Flushes all bytes in the given connection's input and output buffers.
     // |connectionId| : The id of the connection.
     // |callback| : Called when the flush is complete.
     static void flush(long connectionId,
                       FlushCallback callback);
   };
 
 };