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

chrome/browser/resources/file_manager/foreground/js/drag_selector.js

 // Copyright 2013 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';
 
 /**
  * Drag selector used on the file list or the grid table.
  * TODO(hirono): Support drag selection for grid view. crbug.com/224832
  * @constructor
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       'mousemove', this.onMouseMoveBound_, true);
   this.target_.ownerDocument.removeEventListener(
       'mouseup', this.onMouseUpBound_, true);
   cr.dispatchSimpleEvent(this.target_, 'dragselectionend');
   this.target_.cachedBounds = null;
   this.target_ = null;
   // The target may select an item by reacting to the mouseup event.
   // This suppress to the selecting behavior.
   event.stopPropagation();
 };