[MD Bookmarks] Scroll list to top on folder change.

chrome/browser/resources/md_bookmarks/list.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.
 
 Polymer({
   is: 'bookmarks-list',
 
   behaviors: [
     bookmarks.StoreClient,
   ],
@@ skipping 14 matching lines @@
       },
     },
 
     /** @private {Array<string>} */
     displayedIds_: {
       type: Array,
       observer: 'onDisplayedIdsChanged_',
     },
 
     /** @private */
-    searchTerm_: String,
+    searchTerm_: {
+      type: String,
+      observer: 'onDisplayedListSourceChange_',
+    },
+
+    /** @private */
+    selectedFolder_: {
+      type: String,
+      observer: 'onDisplayedListSourceChange_',
+    },
   },
 
   listeners: {
     'click': 'deselectItems_',
   },
 
   attached: function() {
     var list = /** @type {IronListElement} */ (this.$.bookmarksCard);
     list.scrollTarget = this;
 
     this.watch('displayedIds_', function(state) {
       return bookmarks.util.getDisplayedList(state);
     });
     this.watch('searchTerm_', function(state) {
       return state.search.term;
     });
+    this.watch('selectedFolder_', function(state) {
+      return state.selectedFolder;
+    });
     this.updateFromStore();
 
     this.$.bookmarksCard.addEventListener(
         'keydown', this.onItemKeydown_.bind(this), true);
   },
 
   /** @return {HTMLElement} */
   getDropTarget: function() {
     return this.$.message;
   },
@@ skipping 22 matching lines @@
                   return {id: id};
                 });
         this.splice.apply(this, [
           'displayedList_', splice.index, splice.removed.length
         ].concat(additions));
       }.bind(this));
     }
   },
 
   /** @private */
+  onDisplayedListSourceChange_: function() {
+    this.scrollTop = 0;
+  },
+
+  /** @private */
   emptyListMessage_: function() {
     var emptyListMessage = this.searchTerm_ ? 'noSearchResults' : 'emptyList';
     return loadTimeData.getString(emptyListMessage);
   },
 
   /** @private */
   isEmptyList_: function() {
     return this.displayedList_.length == 0;
   },
 
@@ skipping 81 matching lines @@
 
     if (!handled) {
       handled = bookmarks.CommandManager.getInstance().handleKeyEvent(
           e, this.getState().selection.items);
     }
 
     if (handled)
       e.stopPropagation();
   },
 });