[FileBrowser] Fixed default hover state.

chrome/browser/resources/file_manager/css/common.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. */
 
 /* This file contains "borrowed" copy of standard styles. To simplify merging,
  * when altering, please preserve original property value by adding comments.
  */
 input.common[type='checkbox'],
 input.common[type='radio'] {
   -webkit-appearance: none;
@@ skipping 151 matching lines @@
   height: 27px;
   line-height: 27px;
   margin: 0 0 0 8px;
   min-width: 54px;
   padding: 0 8px;
   position: relative;
   text-align: center;
   z-index: 1;
 }
 
+.buttonbar button:hover {
+  -webkit-transition: all 0;
+  background-image: -webkit-linear-gradient(top, #F8F8F8, #F1F1F1);
+  border: 1px solid #C6C6C6;
+  box-shadow: 0 1px 1px rgba(0, 0, 0, 0.1);
+  color: #222;
+}
+
+.buttonbar button:active {
+  background-color: #F6F6F6;
+  background-image: -webkit-linear-gradient(top,#F6F6F6,#F1F1F1);
+  box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.1);
+}
+
 .buttonbar button[disabled] {
   background-color: #EEE;
   background-image: -webkit-linear-gradient(top, #EEE, #E0E0E0);
   border: 1px solid #CCC;
   color: #333;
 }
 
 .buttonbar button:active img {
   opacity: 1.0;
 }
@@ skipping 73 matching lines @@
 menu.chrome-menu > :not(hr)[checked] {
   background-image: -webkit-image-set(
     url('../images/common/check_no_box.png') 1x,
     url('../images/common/2x/check_no_box.png') 2x);
   background-position: 2px center;
 }
 
 menu.chrome-menu > [checked]:before {
   display: none;
 }