Truncating file name in the bottom panel.

chrome/browser/resources/file_manager/css/file_manager.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.
  */
 
 /* Outer frame of the dialog. */
 body {
    -webkit-box-flex: 1;
    -webkit-box-orient: vertical;
@@ skipping 1015 matching lines @@
   white-space: nowrap;
   padding-right: 5px;
 }
 
 .task-item > img {
   -webkit-margin-end: 5px;
 }
 
 /* The selection summary text at the bottom of the preview pane. */
 .preview-summary {
+  -webkit-box-flex: 1;
   color: #666666;
   overflow: hidden;
   padding: 5px;
   text-overflow: ellipsis;
   white-space: nowrap;
   vertical-align: middle;
 }
 
 .dialog-footer .filename-label {
   -webkit-box-orient: horizontal;
@@ skipping 52 matching lines @@
 
 div.offline {
   -webkit-box-pack: center;
   display: -webkit-box;
 }
 
 div.offline > * {
   -webkit-box-align: center;
   display: -webkit-box;
 }