MD Settings: Fix popstate behavior from section route to section route.

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
  */
 var MainPageBehaviorImpl = {
   /** @type {?HTMLElement} The scrolling container. */
   scroller: null,
 
   /** @override */
   attached: function() {
     if (this.domHost && this.domHost.parentNode.tagName == 'PAPER-HEADER-PANEL')
       this.scroller = this.domHost.parentNode.scroller;
     else
       this.scroller = document.body; // Used in unit tests.
   },
 
   /**
    * @param {!settings.Route} newRoute
    * @param {settings.Route} oldRoute
    */
   currentRouteChanged: function(newRoute, oldRoute) {
+    // Scroll to the section except for back/forward. Also scroll for any
+    // back/forward navigations that are in-page.
+    var oldRouteWasSection =
+        !!oldRoute && !!oldRoute.parent && !!oldRoute.section &&
+        oldRoute.parent.section != oldRoute.section;
+    var scrollToSection =
+        !settings.lastRouteChangeWasPopstate() || oldRouteWasSection;
+
     // If this is the first route, or the page was hidden, allow the page to
     // render before expanding the section.
     if (!oldRoute && newRoute.contains(settings.getCurrentRoute()) ||
         this.scrollHeight == 0) {
-      setTimeout(this.tryTransitionToSection_.bind(this));
+      setTimeout(this.tryTransitionToSection_.bind(this, scrollToSection));
     } else {
-      this.tryTransitionToSection_();
+      this.tryTransitionToSection_(scrollToSection);
     }
   },
 
   /**
    * If possible, transitions to the current route's section (by expanding or
    * scrolling to it). If another transition is running, finishes or cancels
    * that one, then schedules this function again. This ensures the current
    * section is quickly shown, without getting the page into a broken state --
    * if currentRoute changes in between calls, just transition to the new route.
+   * @param {boolean} scrollToSection
    * @private
    */
-  tryTransitionToSection_: function() {
+  tryTransitionToSection_: function(scrollToSection) {
     var currentRoute = settings.getCurrentRoute();
     var currentSection = this.getSection(currentRoute.section);
 
     // If an animation is already playing, try finishing or canceling it.
     if (this.currentAnimation_) {
       this.maybeStopCurrentAnimation_();
       // Either way, this function will be called again once the current
       // animation ends.
       return;
     }
 
     var promise;
     var expandedSection = /** @type {?SettingsSectionElement} */(
         this.$$('settings-section.expanded'));
     if (expandedSection) {
       // If the section shouldn't be expanded, collapse it.
       if (!currentRoute.isSubpage() || expandedSection != currentSection) {
         promise = this.collapseSection_(expandedSection);
         // Scroll to the collapsed section.
-        if (currentSection && !settings.lastRouteChangeWasPopstate())
+        if (currentSection && scrollToSection)
           currentSection.scrollIntoView();
       } else {
         // Scroll to top while sliding to another subpage.
         this.scroller.scrollTop = 0;
       }
     } else if (currentSection) {
       // Expand the section into a subpage or scroll to it on the main page.
       if (currentRoute.isSubpage())
         promise = this.expandSection_(currentSection);
-      else if (!settings.lastRouteChangeWasPopstate())
+      else if (scrollToSection)
         currentSection.scrollIntoView();
     }
 
     // When this animation ends, another may be necessary. Call this function
     // again after the promise resolves.
     if (promise)
-      promise.then(this.tryTransitionToSection_.bind(this));
+      promise.then(this.tryTransitionToSection_.bind(this, scrollToSection));
   },
 
   /**
    * If the current animation is inconsistent with the current route, stops the
    * animation by finishing or canceling it so the new route can be animated to.
    * @private
    */
   maybeStopCurrentAnimation_: function() {
     var currentRoute = settings.getCurrentRoute();
     var animatingSection = /** @type {?SettingsSectionElement} */(
@@ skipping 165 matching lines @@
     return /** @type {?SettingsSectionElement} */(
         this.$$('settings-section[section="' + section + '"]'));
   },
 };
 
 /** @polymerBehavior */
 var MainPageBehavior = [
   settings.RouteObserverBehavior,
   MainPageBehaviorImpl,
 ];