MD Settings: Prevent unexpected scrolling to section on popstates.

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.
 
 /**
  * Calls |readyTest| repeatedly until it returns true, then calls
  * |readyCallback|.
  * @param {function():boolean} readyTest
  * @param {!Function} readyCallback
  */
@@ skipping 70 matching lines @@
     }
 
     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)
+        if (currentSection && !settings.lastRouteChangeWasPopstate())
           currentSection.scrollIntoView();
       }
     } 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
+      else if (!settings.lastRouteChangeWasPopstate())
         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));
   },
 
   /**
@@ skipping 112 matching lines @@
       return Promise.resolve();
     }
 
     // Play the actual collapse animation.
     return new Promise(function(resolve, reject) {
       // Wait for the other sections to show up so we can scroll properly.
       setTimeout(function() {
         var newSection = settings.getCurrentRoute().section &&
             this.getSection(settings.getCurrentRoute().section);
 
-        // Scroll to the section if indicated by the route. TODO(michaelpg): Is
-        // this the right behavior, or should we return to the previous scroll
-        // position?
-        if (newSection)
-          newSection.scrollIntoView();
-        else
-          this.scroller.scrollTop = this.origScrollTop_;
+        this.scroller.scrollTop = this.origScrollTop_;
 
         this.currentAnimation_ = section.animateCollapse(
             /** @type {!HTMLElement} */(this.scroller));
 
         this.currentAnimation_.finished.catch(function() {
           // The collapse was canceled, so the page is showing a subpage still.
           this.fire('subpage-expand');
         }.bind(this)).then(function() {
           // Clean up after the animation succeeds or cancels.
           section.setFrozen(false);
@@ skipping 50 matching lines @@
       this.scroller.style.width = 'calc(100% - ' + scrollbarWidth + 'px)';
     }
   }
 };
 
 /** @polymerBehavior */
 var MainPageBehavior = [
   settings.RouteObserverBehavior,
   MainPageBehaviorImpl,
 ];