[FileBrowser] Restored visibility of eject button on unselected removable drives.

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. */
 
 html {
   height: 100%;
 }
 
 html.col-resize * {
   cursor: col-resize !important;
@@ skipping 293 matching lines @@
 div.root-eject {
   -webkit-transition: opacity 70ms linear;
   background-image: -webkit-image-set(
     url('../images/files/ui/eject.png') 1x,
     url('../images/files/ui/2x/eject.png') 2x);
   background-position: center center;
   background-repeat: no-repeat;
   cursor: pointer;
   height: 20px;
   margin-right: 6px;
-  opacity: 0;
+  opacity: 0.7;
   width: 20px;
 }
 
 div.root-eject:hover {
   opacity: 1;
 }
 
 .root-item[selected] > div.root-eject:not(:hover),
 .root-item:hover > div.root-eject:not(:hover) {
   opacity: 0.7;
@@ skipping 1289 matching lines @@
 }
 
 #new-folder {
   margin-right: 30px;
 }
 
 #default-action-dialog {
   min-width: 300px;
   width: auto;
 }