Fix issue caused by updating list that references global scroll target.

chrome/browser/resources/settings/global_scroll_target_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.
 
 /**
  * @fileoverview |GlobalScrollTargetBehavior| allows an element to be aware of
- * the global scroll target. |scrollTarget| will be populated async by
- * |setGlobalScrollTarget|. |setGlobalScrollTarget| should only be called once.
+ * the global scroll target.
+ *
+ * |scrollTarget| will be populated async by |setGlobalScrollTarget|.
+ *
+ * |subpageScrollTarget| will be equal to the |scrollTarget|, but will only be
+ * populated when the current route is the |subpageRoute|.
+ *
+ * |setGlobalScrollTarget| should only be called once.
  */
 
 cr.define('settings', function() {
   var scrollTargetResolver = new PromiseResolver();
 
   /** @polymerBehavior */
-  var GlobalScrollTargetBehavior = {
+  var GlobalScrollTargetBehaviorImpl = {
     properties: {
       /**
        * Read only property for the scroll target.
        * @type {HTMLElement}
        */
       scrollTarget: {
         type: Object,
         readOnly: true,
       },
+
+      /**
+       * Read only property for the scroll target that a subpage should use.
+       * It will be set/cleared based on the current route.
+       * @type {HTMLElement}
+       */
+      subpageScrollTarget: {
+        type: Object,
+        computed: 'getActiveTarget_(scrollTarget, active_)',
+      },
+
+      /**
+       * The |subpageScrollTarget| should only be set for this route.
+       * @type {settings.Route}
+       * @private
+       */
+      subpageRoute: Object,
+
+      /** Whether the |subpageRoute| is active or not. */
+      active_: Boolean,
     },
 
     /** @override */
     attached: function() {
       scrollTargetResolver.promise.then(this._setScrollTarget.bind(this));
     },
+
+    /** @param {!settings.Route} route */
+    currentRouteChanged: function(route) {
+      this.active_ = route == this.subpageRoute;
+    },
+
+    /**
+     * Returns the target only when the route is active.
+     * @param {HTMLElement} target
+     * @param {boolean} active
+     * @return {?HTMLElement}
+     * @private
+     */
+    getActiveTarget_: function(target, active) {
+      return active ? target : null;
+    },
   };
 
   /**
    * This should only be called once.
    * @param {HTMLElement} scrollTarget
    */
   var setGlobalScrollTarget = function(scrollTarget) {
     scrollTargetResolver.resolve(scrollTarget);
   };
 
   return {
-    GlobalScrollTargetBehavior: GlobalScrollTargetBehavior,
+    GlobalScrollTargetBehaviorImpl: GlobalScrollTargetBehaviorImpl,
     setGlobalScrollTarget: setGlobalScrollTarget,
+    scrollTargetResolver: scrollTargetResolver,
   };
 });
+
+// This is done to make the closure compiler happy: it needs fully qualified
+// names when specifying an array of behaviors.
+/** @polymerBehavior */
+settings.GlobalScrollTargetBehavior =
+    [settings.RouteObserverBehavior, settings.GlobalScrollTargetBehaviorImpl];