MD Settings: Custom expand/collapse section animations.

chrome/browser/resources/settings/advanced_page/advanced_page.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.
 
 /**
  * @fileoverview
  * 'settings-advanced-page' is the settings page containing the advanced
  * settings.
  *
  * Example:
@@ skipping 21 matching lines @@
 
     /**
      * The current active route.
      */
     currentRoute: {
       type: Object,
       notify: true,
     },
   },
 
-  behaviors: [I18nBehavior, SettingsPageVisibility],
+  /**
+   * @type {string} Selector to get the sections.
+   * TODO(michaelpg): replace duplicate docs with @override once b/24294625
+   * is fixed.
+   */
+  sectionSelector: 'settings-section',
+
+  /** @override */
+  attached: function() {
+    /** @override */
+    this.scroller = this.parentElement;
+  },
+
+  behaviors: [I18nBehavior, SettingsPageVisibility, RoutableBehavior],
 });