[MD settings] limit scope of subpage animating attribute

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 67 matching lines @@
         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).
     // Also always scroll when coming from either the About or root page.
     var scrollToSection = !settings.lastRouteChangeWasPopstate() ||
         oldRouteWasSection || oldRoute == settings.Route.BASIC ||
         oldRoute == settings.Route.ABOUT;
 
-    if (oldRoute && (oldRoute.isSubpage() || newRoute.isSubpage()))
+    // TODO(dschuyler): This doesn't set the flag in the case of going to or
+    // from the main page. It seems sensible to set the flag in those cases,
+    // unfortunately bug 708465 happens. Figure out why that is and then set
+    // this flag more broadly.
+    if (oldRoute && oldRoute.isSubpage() && newRoute.isSubpage())
       this.isSubpageAnimating = true;
 
     // 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 246 matching lines @@
     return /** @type {?SettingsSectionElement} */(
         this.$$('settings-section[section="' + section + '"]'));
   },
 };
 
 /** @polymerBehavior */
 var MainPageBehavior = [
   settings.RouteObserverBehavior,
   MainPageBehaviorImpl,
 ];