Gallery: Add items to GalleryDataModel before loading their metadata.

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 974 matching lines @@
   } else if (loadType === ImageView.LoadType.OFFLINE) {
     this.errorBanner_.show('GALLERY_IMAGE_OFFLINE');
   }
 
   ImageUtil.metrics.recordUserAction(ImageUtil.getMetricName('View'));
 
   var toMillions = function(number) {
     return Math.round(number / (1000 * 1000));
   };
 
-  ImageUtil.metrics.recordSmallCount(ImageUtil.getMetricName('Size.MB'),
-      toMillions(item.getMetadataItem().size));
+  var metadata = item.getMetadataItem();
+  if (metadata) {
+    ImageUtil.metrics.recordSmallCount(ImageUtil.getMetricName('Size.MB'),
+        toMillions(metadata.size));
+  }
 
   var canvas = this.imageView_.getCanvas();
   ImageUtil.metrics.recordSmallCount(ImageUtil.getMetricName('Size.MPix'),
       toMillions(canvas.width * canvas.height));
 
   var extIndex = entry.name.lastIndexOf('.');
   var ext = extIndex < 0 ? '' :
       entry.name.substr(extIndex + 1).toLowerCase();
   if (ext === 'jpeg') ext = 'jpg';
   ImageUtil.metrics.recordEnum(
@@ skipping 848 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();
 };