Move Files.app files to ui/file_manager

ui/file_manager/file_manager/foreground/css/combobutton.css

 /* 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. */
 
 .buttonbar button.combobutton {
   -webkit-box-align: stretch;
   display: -webkit-box;
 }
 
 .buttonbar .combobutton > .action {
@@ skipping 14 matching lines @@
   display: none;
 }
 
 .buttonbar .combobutton > div > span.disclosureindicator {
   -webkit-transform: rotate(90deg);
 }
 
 .buttonbar .combobutton[hidden] {
   display: none;
 }