Introduce a priority queue to the image loader.

chrome/browser/resources/file_manager/js/photo/mosaic_mode.js

 // Copyright (c) 2012 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.
 
 'use strict';
 
 /**
  * @param {Element} container Content container.
  * @param {cr.ui.ArrayDataModel} dataModel Data model.
  * @param {cr.ui.ListSelectionModel} selectionModel Selection model.
@@ skipping 1697 matching lines @@
  * Initializes the thumbnail in the tile. Does not load an image, but sets
  * target dimensions using metadata.
  *
  * @param {Object} metadata Metadata object.
  * @param {function()} onImageMeasured Image measured callback.
  */
 Mosaic.Tile.prototype.init = function(metadata, onImageMeasured) {
   this.markUnloaded();
   this.left_ = null;  // Mark as not laid out.
 
+  // Set higher priority for the selected elements to load them first.
+  var priority = this.getAttribute('selected') ? 1 : 2;
+
   // Use embedded thumbnails on Drive, since they have higher resolution.
   this.thumbnailLoader_ = new ThumbnailLoader(
       this.getItem().getUrl(),
       ThumbnailLoader.LoaderType.CANVAS,
       metadata,
       undefined,  // Media type.
       FileType.isOnDrive(this.getItem().getUrl()) ?
           ThumbnailLoader.UseEmbedded.USE_EMBEDDED :
-          ThumbnailLoader.UseEmbedded.NO_EMBEDDED);
+          ThumbnailLoader.UseEmbedded.NO_EMBEDDED,
+      priority);
 
   var setDimensions = function(width, height) {
     if (width > height) {
       if (width > Mosaic.Tile.MAX_CONTENT_SIZE) {
         height = Math.round(height * Mosaic.Tile.MAX_CONTENT_SIZE / width);
         width = Mosaic.Tile.MAX_CONTENT_SIZE;
       }
     } else {
       if (height > Mosaic.Tile.MAX_CONTENT_SIZE) {
         width = Math.round(width * Mosaic.Tile.MAX_CONTENT_SIZE / height);
@@ skipping 136 matching lines @@
   return new Rect(this.left_ - this.container_.scrollLeft, this.top_,
       this.width_, this.height_).inflate(-margin, -margin);
 };
 
 /**
  * @return {number} X coordinate of the tile center.
  */
 Mosaic.Tile.prototype.getCenterX = function() {
   return this.left_ + Math.round(this.width_ / 2);
 };