Added "select all/none" checkbox.

chrome/browser/resources/file_manager/css/file_manager.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.
  */
 
 /* Outer frame of the dialog. */
 body {
    -webkit-box-flex: 1;
    -webkit-box-orient: vertical;
@@ skipping 360 matching lines @@
 
 .detail-table li.table-row .table-row-cell:first-child div {
   margin: 0px;
 }
 
 .file-checkbox {
   position: relative;
   z-index: 2;
   -webkit-margin-end: 0px;
   margin-top: 6px;
+  margin-left: 7px;
   opacity: 0.1;
 }
 
+#select-all-checkbox {
+  margin: 0;
+}
+
 li.thumbnail-item .file-checkbox {
   opacity: 0;
 }
 
 li.table-row:hover .file-checkbox,
 li.thumbnail-item:hover .file-checkbox {
   opacity: 0.5;
 }
 
 .file-checkbox:hover,
@@ skipping 185 matching lines @@
 /* Overlay pane covering the entire file manager window (e.g. image editor)*/
 .overlay-pane {
   position: absolute;
   top: 0;
   left: 0;
   width: 100%;
   height: 100%;
   border: none;
   z-index: 100;
 }