MD Settings: Fix scrolling when navigating Forwards from BASIC page.

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

 // Copyright 2016 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.
 
 /**
  * Responds to route changes by expanding, collapsing, or scrolling to sections
  * on the page. Expanded sections take up the full height of the container. At
  * most one section should be expanded at any given time.
  * @polymerBehavior MainPageBehavior
  */
@@ skipping 32 matching lines @@
     var oldRouteWasSection =
         !!oldRoute && !!oldRoute.parent && !!oldRoute.section &&
         oldRoute.parent.section != oldRoute.section;
 
     if (oldRouteWasSection && newRoute == settings.Route.BASIC) {
       this.scroller.scrollTop = 0;
       return;
     }
 
     var scrollToSection =
-        !settings.lastRouteChangeWasPopstate() || oldRouteWasSection;
+        !settings.lastRouteChangeWasPopstate() || oldRouteWasSection ||
+        oldRoute == settings.Route.BASIC;

[Dan Beam, 2016/12/16 00:59:59]

can you explain why?

[tommycli, 2016/12/16 20:17:40]

Done. Refactored a bit and expanded comment.

 
     // For previously uncreated pages (including on first load), allow the page
     // to render before scrolling to or expanding the section.
     if (!oldRoute || this.scrollHeight == 0)
       setTimeout(this.tryTransitionToSection_.bind(this, scrollToSection));
     else
       this.tryTransitionToSection_(scrollToSection);
   },
 
   /**
@@ skipping 234 matching lines @@
     return /** @type {?SettingsSectionElement} */(
         this.$$('settings-section[section="' + section + '"]'));
   },
 };
 
 /** @polymerBehavior */
 var MainPageBehavior = [
   settings.RouteObserverBehavior,
   MainPageBehaviorImpl,
 ];