MD Settings: About page, setup for showing a sub-page.

chrome/browser/resources/settings/settings_page/settings_router.js

 // Copyright 2015 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.
 
 /**
  * @typedef {{
  *   url: string,
  *   page: string,
  *   section: string,
  *   subpage: !Array<string>,
@@ skipping 83 matching lines @@
       page: 'basic',
       section: '',
       subpage: [],
     },
     {
       url: '/help',
       page: 'about',
       section: '',
       subpage: [],
     },
+<if expr="chromeos">
+    {
+      url: '/help/details',
+      page: 'about',
+      section: 'about',
+      subpage: ['detailed-build-info'],
+    },
+</if>
     {
       url: '/advanced',
       page: 'advanced',
       section: '',
       subpage: [],
     },
 <if expr="chromeos">
     {
       url: '/internet',
       page: 'basic',
@@ skipping 425 matching lines @@
           window.history.replaceState(historicState, document.title);
         }
 
         return;
       }
     }
 
     assertNotReached('Route not found: ' + JSON.stringify(newRoute));
   },
 });