MD Settings: Fix scroll when navigating from subpage to About and back.

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 49 matching lines @@
 
   /**
    * @param {!settings.Route} newRoute
    * @param {settings.Route} oldRoute
    */
   currentRouteChanged: function(newRoute, oldRoute) {
     var oldRouteWasSection =
         !!oldRoute && !!oldRoute.parent && !!oldRoute.section &&
         oldRoute.parent.section != oldRoute.section;
 
-    // Always scroll to the top if navigating from a section to the root route
-    // or when navigating to the About page.
-    if (this.scroller &&
-        ((oldRouteWasSection && newRoute == settings.Route.BASIC) ||
-         newRoute == settings.Route.ABOUT)) {
-      this.scroller.scrollTop = 0;
-      return;
+    if (this.scroller) {
+      // When navigating from a section to the root route, we just need to
+      // scroll to the top, and can early exit afterwards.
+      if (oldRouteWasSection && newRoute == settings.Route.BASIC) {
+        this.scroller.scrollTop = 0;
+        return;
+      }
+
+      // When navigating to the About page, we need to scroll to the top, and
+      // still do the rest of section management.
+      if (newRoute == settings.Route.ABOUT)
+        this.scroller.scrollTop = 0;
     }
 
     // Scroll to the section except for back/forward. Also scroll for any
     // in-page back/forward navigations (from a section or the root page).
     var scrollToSection =
         !settings.lastRouteChangeWasPopstate() || oldRouteWasSection ||
         oldRoute == settings.Route.BASIC;
 
     if (oldRoute && (oldRoute.isSubpage() || newRoute.isSubpage()))
       this.isSubpageAnimating = true;
@@ skipping 253 matching lines @@
     return /** @type {?SettingsSectionElement} */(
         this.$$('settings-section[section="' + section + '"]'));
   },
 };
 
 /** @polymerBehavior */
 var MainPageBehavior = [
   settings.RouteObserverBehavior,
   MainPageBehaviorImpl,
 ];