Files.app: Fix closure error which will raised by the updated compiler.

ui/file_manager/gallery/js/slide_mode.js

 // Copyright 2014 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.
 
 /**
  * Slide mode displays a single image and has a set of controls to navigate
  * between the images and to edit an image.
  *
  * @param {!HTMLElement} container Main container element.
  * @param {!HTMLElement} content Content container element.
@@ skipping 542 matching lines @@
     // Note that the SlideMode object is not listening to selection change yet.
     this.select(Math.max(0, this.getSelectedIndex()));
 
     // Show the selected item ASAP, then complete the initialization
     // (loading the ribbon thumbnails can take some time).
     var selectedItem = this.getSelectedItem();
     this.displayedItem_ = selectedItem;
 
     // Load the image of the item.
     this.loadItem_(
-        selectedItem,
+        assert(selectedItem),
         zoomFromRect ?
             this.imageView_.createZoomEffect(zoomFromRect) :
             new ImageView.Effect.None(),
         displayCallback,
         function(loadType, delay) {
           fulfill(delay);
         });
   }.bind(this)).then(function(delay) {
     // Turn the mode active.
     this.active_ = true;
@@ skipping 1291 matching lines @@
   var event = assertInstanceof(event, MouseEvent);
   var viewport = this.slideMode_.getViewport();
   if (!this.enabled_ || !viewport.isZoomed())
     return;
   this.stopOperation();
   viewport.setOffset(
       viewport.getOffsetX() + event.wheelDeltaX,
       viewport.getOffsetY() + event.wheelDeltaY);
   this.slideMode_.applyViewportChange();
 };