[Files.app] Split the JavaScript files into subdirectories: common, background, and foreground

chrome/browser/resources/file_manager/foreground/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 1993 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);
 };