Disable Delete option for custom wallpapers when 'Surprise Me' is enabled.

chrome/browser/resources/chromeos/wallpaper_manager/css/wallpaper_manager.css

 /* Copyright (c) 2013 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. */
 
 html {
   height: 100%;
 }
 
 body {
   -webkit-app-region: drag;
@@ skipping 255 matching lines @@
   width: 240px;
 }
 
 /* [hidden] does display:none, but its priority is too low. */
 [hidden],
 body[custom] [visibleif]:not([visibleif~='custom']),
 body:not([custom]) [visibleif~='custom'] {
   display: none !important;
 }
 
+body[surprise-me-disabled] [visibleif]:not([visibleif~='surprise-me-disabled']),
+body:not([surprise-me-disabled]) [visibleif~='surprise-me-disabled'] {
+  display: none !important;
+}
+
 .progress-bar {
   background-color: rgba(255, 255, 255, 0.7);
   height: 6px;
   position: absolute;
   top: 62px;
   width: 100%;
 }
 
 .progress-track {
   -webkit-transition: width 1ms linear;
@@ skipping 77 matching lines @@
   margin-right: 4px;
   opacity: 0.7;
   position: relative;
   top: 4px;
   width: 17px;
 }
 
 #surprise-me #checkbox.checked {
   background-image: url(../images/ui/checkbox_checked.png);
 }