[cros,webui] Adds scrollbar for the network drop-down controller.

chrome/browser/resources/chromeos/login/network_dropdown.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.
  *
  * This is the stylesheet used by the network drop-down control.
  */
 
 .dropdown-title {
   -webkit-border-radius: 2px;
   -webkit-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
@@ skipping 24 matching lines @@
 .dropdown-title:hover {
   -webkit-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
   background-image: url('../../shared/images/select.png'),
                     -webkit-linear-gradient(#fefefe, #f8f8f8 40%, #e9e9e9);
   color: #333;
   background-position: center right;
   background-repeat: no-repeat;
 }
 
 .dropdown-title img {
-  maring-top: -1px;
+  margin-top: -1px;
 }
 
 .dropdown-title div {
+  -webkit-box-flex: 1;
   margin-top: 1px;
+  overflow: hidden;
+  text-overflow: ellipsis;
 }
 
 .dropdown-container {
   background: #f7f7f7;
   border: 1px solid #7c91bf;
+  max-height: 330px;
+  overflow-x: hidden;
+  overflow-y: auto;
   padding-bottom: 2px;
   padding-top: 2px;
   position: relative;
   top: 100%;
-  width: 248px;
   z-index: 10;
 }
 
 .dropdown-item-container {
-  -webkitpadding-start: 5px;
+  -webkit-padding-start: 5px;
   display: -webkit-box;
   height: 24px;
 }
 
 .dropdown-item-container.hover {
   background: #dce4fa;
 }
 
-.dropdown-image {
-  width: 24px;
-}
-
 .dropdown-item {
+  -webkit-box-flex: 1;
   cursor: default;
   color: #555;
   overflow: hidden;
   padding-top: 4px;
   text-overflow: ellipsis;
   white-space: nowrap;
-  width: 219px;
 }
 
 .dropdown-divider {
   height: 3px;
 }
 
 .dropdown-divider hr {
   -webkit-margin-before: 2px;
   -webkit-margin-after: 2px;
 }
 
 .dropdown-item.disabled-item {
   color: graytext;
 }
 
 .dropdown-overlay {
   bottom: 0;
   left: 0;
   position: fixed;
   right: 0;
   top: 0;
   z-index: 5;
 }