WebUI: fix error in Grid.getItemsInViewPort preventing correct layout.

chrome/browser/resources/shared/js/cr/ui/grid.js

 // Copyright (c) 2011 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.
 
 // require: list_selection_model.js
 // require: list_selection_controller.js
 // require: list.js
 
 /**
  * @fileoverview This implements a grid control. Grid contains a bunch of
@@ skipping 150 matching lines @@
     getItemsInViewPort: function(scrollTop, clientHeight) {
       var itemHeight = this.getDefaultItemHeight_();
       var firstIndex =
           this.autoExpands ? 0 : this.getIndexForListOffset_(scrollTop);
       var columns = this.columns;
       var count = this.autoExpands_ ? this.dataModel.length : Math.max(
           columns * (Math.ceil(clientHeight / itemHeight) + 1),
           this.countItemsInRange_(firstIndex, scrollTop + clientHeight));
       count = columns * Math.ceil(count / columns);
       count = Math.min(count, this.dataModel.length - firstIndex);
-      return count;
+      return {
+        first: firstIndex,
+        length: count,
+        last: firstIndex + count - 1
+      };
     },
 
     /**
      * Adds items to the list and {@code newCachedItems}.
      * @param {number} firstIndex The index of first item, inclusively.
      * @param {number} lastIndex The index of last item, exclusively.
      * @param {Object.<string, ListItem>} cachedItems Old items cache.
      * @param {Object.<string, ListItem>} newCachedItems New items cache.
      * @override
      */
@@ skipping 110 matching lines @@
       return index + 1;
     }
   };
 
   return {
     Grid: Grid,
     GridItem: GridItem,
     GridSelectionController: GridSelectionController
   }
 });