Fix style on network details to put scrollbar in tab contents.

chrome/browser/resources/options2/subpages_tab_controls.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. */
 
 .subpages-nav-tabs .tab {
   padding: 4px 8px;
   position: relative;
 }
 
 .subpages-nav-tabs .active-tab {
@@ skipping 32 matching lines @@
 /* .tab is not removed when .active-tab is added, so we must
  * override the hidden visibility above in the active tab case.
  */
 .subpages-nav-tabs .active-tab .active-tab-label {
   visibility: visible;
 }
 
 .subpages-nav-tabs {
   background: -webkit-linear-gradient(white, #F3F3F3);  /* very light gray */
   border-bottom: 1px solid #A0A0A0;  /* light gray */
-  margin-bottom: 15px;
   padding: 4px;
 }
 
 .subpages-tab-contents {
    -webkit-padding-start: 10px;
   display: none;
+  padding-top: 15px;
 }
 
 .active-tab-contents {
   display: block;
 }