Remove dangling chrome://theme/IDR_CLOSE_BAR* references

chrome/browser/resources/shared/css/expandable_bubble.css

 /* Copyright (c) 2011 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.
  */
 
 .expandable-bubble {
   -webkit-border-image: url('chrome://theme/IDR_APP_NOTIFICATION_SMALL_BUBBLE')
                         5 5 7 6 stretch;
   -webkit-box-sizing: border-box;
   -webkit-user-select: none;
@@ skipping 56 matching lines @@
 .expandable-bubble[expanded] {
   padding: 3px;
   z-index: 3;  /* One higher then the close button on an unexpanded bubble. */
 }
 
 .expandable-bubble[expanded] > .expandable-bubble-close {
   z-index: 4;
 }
 
 .expandable-bubble-close {
-  background-image: url('chrome://theme/IDR_CLOSE_BAR');
+  background-image: url('../../../../../ui/resources/close_bar.png');
 }
 
 .expandable-bubble-close:hover {
-  background-image: url('chrome://theme/IDR_CLOSE_BAR_H');
+  background-image: url('../../../../../ui/resources/close_bar_h.png');
 }
 
 .expandable-bubble-close:active {
-  background-image: url('chrome://theme/IDR_CLOSE_BAR_P');
+  background-image: url('../../../../../ui/resources/close_bar_p.png');
 }