Avoid UI unresponsiveness when switching between large images.

ui/file_manager/gallery/js/gallery_item.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.
 
 /**
  * Object representing an image item (a photo).
  *
  * @param {!FileEntry} entry Image entry.
  * @param {!EntryLocation} locationInfo Entry location information.
  * @param {MetadataItem} metadataItem
@@ skipping 422 matching lines @@
         return Promise.reject(str('GALLERY_FILE_EXISTS'));
       }, function() {
         return new Promise(
             this.entry_.moveTo.bind(this.entry_, parentDirectory, newFileName));
       }.bind(this));
     }.bind(this));
   }.bind(this)).then(function(entry) {
     this.entry_ = entry;
   }.bind(this));
 };
+
+/**
+ * The threshold size of an image in pixels, which we always use thumbnail
+ * image for slide-in animation above this. This is a hack to avoid an UI
+ * unresponsiveness when switching between images.
+ * @type {number}
+ * @const
+ */
+GalleryItem.HEAVY_RENDERING_THRESHOLD_PIXELS = 4000 * 3000;
+
+/**
+ * Whether the image requires long rendering time.
+ *
+ * @return {boolean}
+ */
+GalleryItem.prototype.requireLongRenderingTime = function() {
+  // Check for undefined values.
+  if (!this.metadataItem_ ||
+      !this.metadataItem_.imageHeight || !this.metadataItem_.imageWidth)
+    return false;
+  var numPixels = this.metadataItem_.imageHeight *
+      this.metadataItem_.imageWidth;
+  return numPixels > GalleryItem.HEAVY_RENDERING_THRESHOLD_PIXELS;
+};