MD Settings: Restore focus when exiting various subpages, part 2.

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 67 matching lines @@
       }
 
 <if expr="_google_chrome and is_macosx">
       #promoteUpdater[disabled] {
         @apply(--settings-secondary);
       }
 </if>
     </style>
     <div>
       <settings-section page-title="$i18n{aboutPageTitle}" section="about">
-        <settings-animated-pages id="pages" section="about">
+        <settings-animated-pages id="pages" section="about"
+            focus-config="[[focusConfig_]]">
           <neon-animatable route-path="default">
             <div class="settings-box two-line">
               <img id="product-logo" on-tap="onProductLogoTap_"
                   srcset="chrome://theme/current-channel-logo@1x 1x,
                           chrome://theme/current-channel-logo@2x 2x"
                   alt="$i18n{aboutProductLogoAlt}">
               <span class="product-title">$i18n{aboutProductTitle}</span>
             </div>
             <div class="settings-box two-line">
               <!-- TODO(dpapad): Investigate why vulcanize does not handle well
@@ skipping 76 matching lines @@
                 on-tap="onReportIssueTap_">
               <div class="start">$i18n{aboutReportAnIssue}</div>
               <button class="subpage-arrow" is="paper-icon-button-light"
                   aria-labelledby="reportIssue"></button>
             </div>
 </if>
 <if expr="chromeos">
             <div class="settings-box" on-tap="onDetailedBuildInfoTap_"
                 actionable>
               <div class="start">$i18n{aboutDetailedBuildInfo}</div>
-              <button class="subpage-arrow" is="paper-icon-button-light"
+              <button id="detailed-build-info-trigger" class="subpage-arrow"
+                  is="paper-icon-button-light"
                   aria-label="$i18n{aboutDetailedBuildInfo}">
               </button>
             </div>
 </if>
             <div class="settings-box padded block copyable">
               <div class="info-section">
                 <div class="secondary">$i18n{aboutProductTitle}</div>
                 <div class="secondary">$i18n{aboutProductCopyright}</div>
               </div>
 
@@ skipping 20 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>