[MD settings] replace secondary-action with separator

chrome/browser/resources/settings/about_page/about_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="about_page_browser_proxy.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../icons.html">
 <link rel="import" href="../lifetime_browser_proxy.html">
 <link rel="import" href="../route.html">
 <link rel="import" href="../settings_page/main_page_behavior.html">
 <link rel="import" href="../settings_page/settings_animated_pages.html">
 <link rel="import" href="../settings_page/settings_section.html">
 <link rel="import" href="../settings_page_css.html">
@@ skipping 106 matching lines @@
                 </div>
                 <span id="deprecationWarning"
                     hidden="[[!obsoleteSystemInfo_.obsolete]]">
                   $i18n{aboutObsoleteSystem}
                   <a href="$i18n{aboutObsoleteSystemURL}" target="_blank">
                     $i18n{learnMore}
                   </a>
                 </span>
                 <div class="secondary copyable">$i18n{aboutBrowserVersion}</div>
               </div>
-              <span id="buttonContainer" class="secondary-action"
-                  hidden="[[!showButtonContainer_]]">
+              <span id="buttonContainer" hidden="[[!showButtonContainer_]]">
+                <div class="separator"></div>
                 <paper-button id="relaunch" class="secondary-button"
                     hidden="[[!showRelaunch_]]" on-tap="onRelaunchTap_">
                   $i18n{aboutRelaunch}
                 </paper-button>
 <if expr="chromeos">
                 <paper-button id="relaunchAndPowerwash" class="secondary-button"
                     hidden="[[!showRelaunchAndPowerwash_]]"
                     on-tap="onRelaunchAndPowerwashTap_">
                   $i18n{aboutRelaunchAndPowerwash}
                 </paper-button>
@@ skipping 79 matching lines @@
               <settings-detailed-build-info></settings-detailed-build-info>
             </settings-subpage>
           </template>
 </if>
         </settings-animated-pages>
       </settings-section>
     </div>
   </template>
   <script src="about_page.js"></script>
 </dom-module>