Revert r154623 - "Adds clouds.png in shared location."

chrome/browser/resources/file_manager/css/gdrive_welcome.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. */
 
 /* Google Drive welcome banners.*/
 .gdrive-welcome-wrapper {
   /* This image looks good in high DPI as is. */
-  background-image: url(chrome://resources/images/clouds.png);
+  background-image: url('../images/files/ui/clouds.png');
   background-repeat: repeat-x;
   color: #333;
 }
 
 .gdrive-welcome-icon {
   background-image: -webkit-image-set(
     url('../images/files/ui/gdrive_logo.png') 1x,
     url('../images/files/ui/2x/gdrive_logo.png') 2x);
   background-repeat: no-repeat;
 }
@@ skipping 160 matching lines @@
   margin-left: 20px;
 }
 
 body:not([type='full-page']) .gdrive-welcome.page .gdrive-welcome-wrapper {
   background-position: 0 0;
 }
 
 body:not([type='full-page']) .gdrive-welcome.page .gdrive-welcome-icon {
   height: 200px;
 }