Reduce usage of webkit CSS prefixes in chrome/browser/resources

chrome/browser/resources/chromeos/login/network_dropdown.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 is the stylesheet used by the network drop-down control. */
 
 .dropdown-title {
   -webkit-appearance: none;
   -webkit-box-align: start;
   -webkit-padding-end: 20px;
@@ skipping 46 matching lines @@
   background-image: url(../../../../../ui/webui/resources/images/select.png),
       linear-gradient(to bottom,
                        rgb(231, 231, 231),
                        rgb(231, 231, 231) 38%,
                        rgb(215, 215, 215));
   box-shadow: none;
   text-shadow: none;
 }
 
 .dropdown-title:focus {
-  -webkit-transition: border-color 200ms;
   border-color: rgb(77, 144, 254);
   outline: none;
+  transition: border-color 200ms;
 }
 
 html[highlight=strong] .dropdown-title:focus {
   box-shadow: 0 0 23px rgb(77, 144, 254);
 }
 
 .dropdown-title img {
   margin-top: -1px;
 }
 
@@ skipping 56 matching lines @@
 }
 
 .dropdown-overlay {
   bottom: 0;
   left: 0;
   position: fixed;
   right: 0;
   top: 0;
   z-index: 5;
 }